Good for you. Rebuild as you need.

The type of fiberglass isn't as important as laying it out properly as in surface prep, poly or epoxy mixing, etc. Scraps may be a pain in the rear to work with and require multiple layups. I used whatever weight of cloth in mine and it required chopped strand mat which was not fun. As to the stringers & hull you'll want a spacer between the wood and hull whether it's foam or something like PL poly adhesive bedding.

Can't speak to the rear locker other than to say in other models it is removable. No idea how different the topcap may or may not be.

Putting back together is 'fun' but all of that happens really quickly once the floor is ready. Be aware that without your floor and topcap the hull has flexed from losing support. You'll want to prop it back up before the floor goes in so the topcap shape more closely matches the hull shape.

Old Supras were engineered like tanks and precision wasn't part of the equation. Shoddy construction was. You can easily do a better job than the factory.