[Christ]

I've had relatively good luck with the Bond-o resin that you can get at Wal-Mart, but I'm not building large panels or stuff like that... I've used it for speaker boxes and replicating small plastic parts for cars that are hard to find (84-87 CRX parts, etc.)

I can't say much about the fabric, b/c I usually use polyester (fleece blankys). I used to get scraps free from hobbyists, and I could usually stretch some of them out enough to make the part.

I, again, can't comment on templates, since I've never did anything one-off that the first application wasn't the final result (speaker box).

I usually apply grease to the original part (or Stoner brand mould release), apply something like greatstuff over it, wait for it to fully cure, remove it from the original piece, and smooth out the inside, changing any features that need to be changed/altered/fixed.

Core, obviously, I am only making the part from fiberglass... the only thing I've ever used for a core was chicken wire, laying fiberglass over and under it, to add strength to the shape.

I think I pretty much covered everything...
Anyway, that's my .02 about it, hope it helped somehow.