Taking the plywood off requires the use of a nail puller to rip the screw/nail things out. I got about half of it pulled off tonight.
The process rips the 1/2" plywood up pretty good, but no so bad as I won't reuse it.
The rib rust actually isn't as bad as I thought, mostly just in a couple places. It will be pretty easy to mitigate and Rustoleum over it.
I've been doing a lot of research on insulation strategies: spray foam, mineral wool, batts, polyiso, XPS, EPS, radiant barrier, etc. For a variety of reasons, I've decided that polyiso is the least bad option. (I really wanted to use Roxul's rock wool rigid board product, but that stuff is so heavy it would completely blow my weight budget).
I also got a quote for my solar system ($1,200) from a guy up near Denver who sources a bunch of his stuff second-hand or canceled orders, etc. He designs the whole system and provides all the various parts, so that's going to be a huge relief in terms of the time I'd have to spend figuring everything out, sourcing every component, etc.