Oh boy, I'll be watching this thread. First, I love the plan you have put together. If you execute this like you intend to, it's going to look awesome! Second, I am facing some of the same challenges in my bath. I've spent an ungodly number of hours measuring, sketching, calculating, and laying out everything to try and make sure it all lines up. There are so many factors to consider, and Bill, Mongo, and others will wave lots of good info for you. I'd love to answer a few of your questions, but I'm going to leave it to the professionals. They would probably have to follow me with corrections anyway.

Be sure and keep us posted on your progress.

Joe

First of all, I have to say I'm very impressed at the detail to which you've thought all this out. It took me a while to read through it, referring back to the pictures, but you really have analyzed this 6 ways from Sunday.

My comments:
1/2: Don't forget the thickness of the thinset too. But you should still be 3/4/5/6: I'd miter the pencil rail and the subway tile. No great tips (I've not done many), just make sure your tile saw accommodates miters.
7: Do a pre-layout so you can see if there will be any really bad stuff, like need for 1/2" tile, and try to rearrange to avoid it. Make the most visible parts look the best, and hide the short stuff in harder-to-see spots.
8: Yes, most important to make the top of those base tiles align.
9/10: The one problem with just shortening all the base tiles (if needed) would be that it looks like you want the lowest row of subway tiles to start above the shower curb. So that's going to be at a fixed height. I would use the small mosaics as the "flex" filler, adding/deleting a row if needed. And for the fine-tune adjusting, rather than having the niche perfectly integrated at the exact width of the chair rail, plan so the bottom is above the chair rail, and have the border tile be a cut-to-fit. Then start at the floor, tile up to the niche, adjust the mosaics as needed for the chair rail to be at the desired height. (BTW, that's quite an impressive integrated design!)
11: Dunno. We've hired our glass doors installed.
12: I'd put the door/window trim on first, then butt the tiles right into them. Caulk the crack.
13: They make special tile drill bits that cut holes.
14: All you can do is lay out a couple rows and if you get small cuts, shift everything a few inches and the small cuts disappear.

Good luck, and make sure to post photos of your progress!

Clumsy, my patuty!! WOW!! Where do you live??? Can I come out and tile your bathroom??? :-)

In all seriousness, that's going to be one sweet masterpiece to put together!

Before I get to your questions, though I do see one problem. It's going to be tough to run the chair rail through the shower and have any kind of glass enclosure. Not impossible, but tough. You would have to work together with your glass guy to figure out EXACTLY where the glass would go, so you could leave notches in the chair rail. I can guarantee you-- they're not going to notch the glass for you. :-)

Now, on to the questions:

#1-6) What you have drawn is excellent. With reference to the subway tile, no, the corner pieces do not need to be mitered. What you can do is cut the pieces, but then turn the cut edge into the field, and use the "factory" edge as the bullnose. Now, I said they don't NEED to be mitered. However, if you'd PREFER to miter them, there's no reason why you couldn't. It's not like it's ceramic where you'd have to worry about a sharp edge. As for the chair rail and liner, you're right. Those WOULD have to be mitered. The biggest tip I could give you about mitering the chair rail would be to have a piece of 2x4 handy with a 45 degree mitered end on it. You can place the mitered side of the 2x4 against the wet saw tray table's edge, and that'll give you the correct angle, and the thickness of the 2x4 will give you something to make sure you're standing the chair rail up straight while you cut it.

If you decide that you want to miter all the outside corner tiles, the only advice I can give you is leave a little "meat" on the edge. You don't want to take the miter all the way to the face of the tile. If you do, you'll end up with an extremely ragged edge. Leave 1/16" of meat or so on the front edge. The finished miter will still look just as tight, and it'll be 100% stronger.

#7) Don't worry about continuing the cuts. Atleast not on the subway tiles. For the most part, the ONLY time you really need to worry about it is when you use a diagonal layout. With running bond (the brick joint pattern), there's no need to continue it. Take each wall individually. Now, the best thing is to center the walls. However, sometimes that gives you small pieces on each end. With a square layout, moving the layout over half a tile, so the tile is centered instead of the grout joint, the problem is solved. With running bond, if you move it over half a tile, it puts you right back where you started!! So how do you move the layout over and still keep it centered? Move it over a QUARTER of a tile (1 1/2"). What this does is it'll give you equal, but alternating cuts. Lay it out on paper and try it-- You'll see what I mean.

#8) Yes, that's normal.

#9) Ya had to give me a hard one!! :-) You're right-- this CAN be tricky. But you're dead on the right track. You need to figure out your coursing (each course is one tile and one grout joint). Lets say yout tile is exactly 3" high, and you're using a 1/4" grout joint. Going by your drawing, I come up with a height of 51 1/2" high. You show a 6x12 piece on the bottomwith the 1/4" joint, that's 6 1/4". Next is 12 courses of subway tile. That's 39 inches (with 12- 1/4" joints). Then the pencil liner, which, if it were me, would get an 1/8" joint (to match the joint in the 3 rows of mosaics), so that's another 1 1/8", and then I'm assuming the chair rail is 2", plus another 1/8" joint, 2 1/8".

Just a side note-- this would be another reason for NOT using the chair rail, unless you have the shelf come out over the top of the chair rail. With the other three sides, you can either cap the edges of the niche pieces, or you can have the niche pieces cap the edges of the wall. But the shelf MUST come over the edge of the wall tile. You want any water running down the face of the tile, rather than going into the grout joint. Alot of times, I'll even use a piece of granite tile, and round it out PAST the face of the tile, so that it doesn't even come doen the face of the tile, but actually gives a drip edge.

Okay-- back to your niche. Just for the sake of argument, lets say the height is 51 1/2". You want to take into account the thickness of the cement board, as well as the kerdi (figure 5/8"). I would also, as you surmised, give it extra as a "fudge" factor . That way if you need the play, it's there, and if you don't, you can always fill it in with thinset. If it were up to me, and the chair rail was definitely going to stay, I'd set the framing at 50 1/2". The only question is, are you going to set your levels off the finished floor, or off the subfloor? Personally, I'd set it off the subfloor, but when I actually set the tile, set it over the finished floor, cutting it in. That way, if the floor's out of level at all, you'll never see it. Either way, it's up to you. The point is, I'd set the bottom of the niche framing an inch below what you expect the actual coursing to be.

#10) That's the way it LOOKS when it's done. :-) You start with a full course above by nailing a piece of wood, and tiling off of that, and then removing it afterward and cutting in the bottom. As for the Kerdi in the shower, you can patch the holes afterward with Kerdi-Fix. You want to wait as long as possible to tile the shower and bathroom floors. You never want to be working over finished work any more than absolutely necessary.

#11) I already addressed this above.

#12) Install your wood trim first and tile to it.

#13) Diamond hole saw. You can check some of the online tile tool supply sites. if you have a hard time locating them, let me know, and I'll see what I can do to find em for you.

#14) this is where we get back to the thing about going from center to 1/4 and 3/4 tiles to get back to center. It works with diagonal layout, too. One other thing to think about, and this would work as a nice design feature, too-- from the chair rail up, turn one row of subway tiles on end, running them lengthwise up the sides of your diagonal tiles as a border.

WOW!! This reminds me of Rodney Dangerfields's movie Back To School-- to paraphrase right after he finishes the oral exam and says "I feel like I just gave birth!! To an apprentice!!"

One other thing, concerning the chair rail and glass-- if you DO decide to keep the chair rail thru the shower, you're going to HAVE to have fixed glass panels coming off both walls. You will have no choice in this matter.

Hi again. I went to bed after posting last night and just now had a chance to get back online.

Joe, Weedy, and Bill, thank you for the positive comments about my design.

Weedy and Bill, thanks so much for the all of the answers and advice. I feel MUCH more confident about being able to decently carry off my plans correctly and nicely.
Before I begin tiling I'm going to print this thread out and have it handy as I begin and as I reach the different critical points.

Bill, I had not considered that the shelf needed to come over the wall tile; I had it the opposite way. Do you know if I can likely get granite tile 20" wide? Especially if I only need one tile? And what do I need to do to the exxposed edge to made it look nice?

Yes, I should definitely run one course of subway tile, on end, at the edge of the diagonal tile above the chair rail; thanks for the advice on this.

Again, thanks to both of you for taking the time to review my design and questions and putting so much into the answers.

I do have a few more questions, but never fear - they are not as detailed or complicated as the earlier ones.

15 - Through the doorway of my bathroom is a carpeted floor - which may one day have hardwood. Should I look for a nice stone threshold for the doorway? I think I noticed some at the tile store. Or is there a better thing to do?

16 - One shower wall is on an exterior wall. I think I read here that if we're using Kerdi on an exterior wall to NOT have a separate vapor barrier. Is this right? So I should put unfaced insulation in the wall with no vapor barrier?

Thanks again! You guys are great!

Bill, I had not considered that the shelf needed to come over the wall tile; I had it the opposite way. Do you know if I can likely get granite tile 20" wide? Especially if I only need one tile? And what do I need to do to the exxposed edge to made it look nice?

What you might do is go to a stone shop and see if they have any remnants that would look good with either your tile, or the overall color scheme of the room, and if they do, you can have them cut it to size, and even put a finish on the outside edge, whether that be bullnose, or even an ogee, or whatever. Going to a stone shop, and using a 2 cm slab piece, you could get even more decorative than I do. Just measure the depth of the nich, including coming out about a 1/2" past the finish directly underneath, whether that be the chair rail or the tile.

#15) A stone threshold is ALWAYS a nice touch, as far as I'm concerned. Puls, if installed properly, it even has a utilitarian purpose-- in case of light flooding-- from the tub or toilet overflow-- it'll act as a dam at the door to keep the floor finishes outside the door from being ruined. You might even see, when you go for the niche piece, if they could make a threshold out of the same stone!

#16) You could either do that, or just cut a bunch of slits into the facing. That way, you still get some protection, but at the same time you don't create a moisture "sandwich".