1939 is just kinda-old. Sounds like it's not gonna make a National
Register.

I'd suggest priorities:
1. repair any structural problems and possible related causes (water
leakage, insufficient foundation support, etc.) as possible first so
you can support loads. If not, find a 'plan-b'.
2. replace all damaged materials.
3. possibly by room, make floor supports level; work up from there
(subfloor, etc.)

I'd be prepared to remove lots of crap, from your statement. Might be
useful in woodstove, anyhow. :")

Seems you'll be buying LOTS of whatever materials you choose. Get
expert advice, and negotiate purchase with REAL lumber-yard. You gonna
do this yourself?

HTH,
J