Here is a shot of where I am at. Note the stairway. From the stairway to the big white pipe I will simply add drywall....no outlets here. From the big white pipe to the copper water meter...more drywall though this will be enclosed as a closet. The water meter over to the other end of the house (9 feet) I plan to stud out, ditto the 12' wall perpendicular to this one. I can add some extra insulation and run some outlets, switches etc.

Note the stairway shot. Note the photo closeup of the sill area as you go up the steps. Should I foam this or caulk it? I can actually see a grey/white wire in there, of the speaker wire sort...not electrical, perhaps the security system...not sure if this factors into foaming, caulking or leaving as is...

I hope I am doing OK.

First pic: run a line of foam down between wood and the wall.

Photo 2: The simplest thing is to put in a piece of XPS, and tape over it with builders tape.

Photo 3: looks like lots of room for drywall over the foam.

Bottom pic: What really works well there is acoustical caulking--a black non-skimming caulk.

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First pic: run a line of foam down between wood and the wall.
**Thought so.

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Photo 2: The simplest thing is to put in a piece of XPS, and tape over it with builders tape.
**Yea but I would be foaming at some point and thought it might be easier to give a shot there in each hole...though I guess I'd have to cut the foam flush and it would make a mess so I think I like your idea better...is that just duct tape you refer too? I do have foam adhesive...could just dab some on the back and stick it in...? I thought I would need the foam adhesive to hold the panels in place while attached them but have found it was not necesary.

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Photo 3: looks like lots of room for drywall over the foam.
**All foam will be drywalled over EXCEPT the last 9 feet (after the water meter coming towards you for 9 feet...not eally shown...I am thinking I will frame here, add some more insulation and some outlets...this is actually the tv area.

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Bottom pic: What really works well there is acoustical caulking--a black non-skimming caulk.
**Ok, I had the canned foam but was not sure how easy it would be to use here so I figured caulk. I will look for the stuff you describe....do you have a brand or do I just look for it in the paint aisle? Likley I should use it on the sill around the perimeter anyway right???....they had fg hanging out of there...I pulled it out. FYI: My intent is to cover this with drywall..somehow....thats my other issue, the area between the stair striger and wall. I am still thinking about that. I may not be able to get the drywall below to match with the drywall already in place above....a job for later though!

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I can't help you with your questions, but what are you doing with the rim joist area?

THIS IS A AN AREA WHERE I HAVE ANOTHER QUESTION!
**To be honest, if you are talking about the area above the XPS, there is fg in there now. Where I have removed the fg it has been pretty airtight unless a pipe or something is there. I will foam that with a can. I guess I will either use my cutoff XPS pieces to make inserts in here then shove the fg back in front of it....IS THAT UP TO CODE?---a dropped ceiling will eventuallly be in place. If not I likely will just put the fg back in place.

PS: looks like pic 1 did not need to be rortated 90 degrees!

Foam works too. Use builder's tape--Tyvek and Tuck are two popular brands.

Acoustical sealant stays flexible and is an excellent air sealer. It's used to seal poly vapour barriers behind drywall. But you can't use it anywhere that is not to be covered. It's messy stuff. LePage and Tremco are two manufacturers.

A minimum of 1" XPS followed by FG works well in a basement according to Building Science Corp.

Other manufacturers include US Gypsum, Titebond and Mono.

If you still can't find any--I suppose a 35 year rubber caulking should work.

That latex caulk is pretty benign on the hands and doesn't stink and doesn't off gas anything flammable that could lit off by the boiler burner.

I've been trying to fit the pieces tightly, which can cause other problems.