Wow.... the year, condition, and vibe of that thing remind me of my 77 targa, which was also sitting for 20 years when I bought it. I rebuilt the calipers using $6 seals and drove it for a few years, and then 2 years ago I tore into it to refresh it properly.
If you want a youtube series focused on actual porsche mechanics, not just generic bodywork progress on a 911, follow my series:
https://youtube.com/playlist?list=PLuUnOD-P-8CEFy0FIS0RUA-fvp4SwZ3_g
I've done everything myself except the trans rebuild.... I suggest you pull the engine/trans, check headstuds, if those are good/holding, do a leak down, and go from there. If you have decent leak down #s and no broken head studs, it's mainly just replacing seals/a lot more affordable. If you have pulled headstuds or need rings... well..... yeah. Bend over.