Rafe- careful with that wagon if you expect to try getting it on the road. Not a bad deal for a parts car with those features in good shape, but "77k miles" could be "177k miles", could be "277k miles", etc...
When you do tear down the interior Rohn, you would probably be fine with just cleaning all the trim instead of painting it. Unless they have some kind of stains, it should look decent with some good vinyl/plastic polish or compound.
Teardown from my experience:
-You can start with removing every trim piece from the hatch area to the dash (don't bother trying to remove the dash if it isn't completely necessary, it's a REAL pain).
-Make sure to leave all the screws in their places after you remove each piece, it can be tough to remember where they go if you don't.
-Once that's finished, you can take off the seat covers, remove the rear seatbacks, then the rear seats.
-The hatch carpet should then come out easily as a single piece.
-The front seat frames might be harder to get off, as the bolts might be a combination of factory rust coating and globs of rust lol. Definitely strip that stuff off before you try removing them, and make certain you have the correct size sockets.
-After the front seat frames are out, the front carpet should come off with a bit of pulling and peeling.
-Inspect every inch for rust, and do what you need to get it fixed.
-Apply a good seam sealer over the factory seams or any new weld seams, because this is often where the rust creeps up.
-Paint over the seams, and anywhere else you feel necessary, with a good rust paint. I've had an EXCELLENT experience with Rust Bullet auto paint, because it brushes on like a dream, requires little preparation, and sinks into the rust (which it CAN be used to paint over, as long as it's not loose). However, it is probably one of the most expensive paints you would buy, at $160/gal. For me, 1pt($35) laid two thick coats over my entire rear hatch floor and some sections of my frame. Very satisfied, but any good rust paint should work fine for your needs.
-Polish and clean everything while it is out of the car. It will be a lot easier than doing it in the car.
It's really cool once you see everything coming together and you can start putting the fresh new interior back in. I can't wait to have my humpty dumpty back together again!