Im remodeling an old log home – I framed 2×4 walls on the interior that are spaced away from the (flat) log anywhere from 1/2″ in spots to 1.5″/2″ in others (the house is old and the logs vary obviously). I was originally thinking of using spray foam in the entire cavity because I want to air seal as much as possible, but then I came across the flash and batt method which would be cheaper for me.

Any issues with doing 2″ of closed cell against the logs and filling the rest with fiberglass?

I also have a full basement underneath and I was planning on using fiberglass in the walls but now i’m a bit confused if that would cause problems since its permeable. The way it stands currently is (from exterior to interior):
– arroyo drainboard
– polywall peel and stick membrane
– concrete wall
– 2″ polyiso
– 2×4 framed wall.

I ran the rigid board an inch of so down from the top of the concrete wall and have the sil plate exposed and was planning on having the spray foam contractor hit that with spray foam as well. Should I flash the exterior side of the 2×4 wall against the rigid board as well to make sure i’m airtight or should I just make sure to tape the seams of the rigid board well and then insulate with whatever I want? Thanks.