You almost have too many questions for a single post - I'll try giving input where I feel qualified. It is good you are planning well in advance. Your "want list" sounds reasonable but I wouldn't give up on the bath. There are up flow toilets (with a self-contained pump) to solve the problem you mention.

1 - A sound plan is essential. Whether or not you hire a designer depends largely on your confidence but in any event you need to imagine YOUR space. We put lots of tape on the floor to mark positions. You can draw to scale on graph paper or use a computer design program. The electrical and plumbing diagrams may be where professional input is needed most.

2 - Beadboard ceilings are nice but you need something to nail or glue onto. Personally, I would be afraid that paneling would warp between spans however others may have experience using it in this manner.

3 - haven't heard of them but wood ceiling panels sound interesting.

4 - I have no knowledge of cork but I would fear depressions from high heals and other sharp objects. We live in northern Illinois and have vinyl tile. It is warmer than the concrete, easy to clean and because the floor is well below the frost line some guests are comfortable in stocking feet. An area rug in from the the TV is very comforting. But, your walk-out basement will most likely be colder on the floor than ours depending on your location.

5 - Radiant heat would be wonderful but I have no knowledge about using it with drycore. Best speak with a representative. If you have concerns about water, I personally would stay away from drycore. The base is partical board which will absorb mositure and fail.

6 - Personally, I would not want a gas fireplace in the basement - either ventless or vented. If you have a group it gets too warm. My fireplace will be electric to enjoy the ambience any time and with a heater should more warmth be necessary.

7 - Tools, depends on what you plan to do yourself. Certainly a good circular saw, drill/hammer drill, level, hammer and the like. Possibly an air compresser and nailer. Electricity requires conduit bender, wire puller and a good set of linemans pliers. Plumbing a torch, hack saw or tubing cutter, file. That is just off the top but there are many more items that will become either necessary or convenient. If you have no tools, the set will be pretty complete when you're finished.

8 - We really have no regrets though some very minor (and personal) modifications would be made if starting over. We did everything DIY over the course of 5 winters which provided time to reason through difficulities or opportunities.

Photos of ours and linked from "My Page" Good luck with yours.

regarding #5 -actually this dricore sub-floor is a 2 part system- a 2X2 particle bd on a layer of plastic "feet" for the any moisture (from leak or concrete)to dry out. The wood never touches the concrete floor.

However, if you have a constant leak - you ought to get it fix first before any type of installation.