If you're hotwirig then you are using EPS. Any imperfections will show up in the final lamination, either as a dark spot or the glass will follow the contour. You can fill in mistakes with a ligtweight spackle...Dap makes one called Fast 'n Final...I use a generic product from ACE hardware. Before you lamiate, you'll want to seal the EPS with this spackle. NOT a thick coat, just enough to slow down the resin penetration into the EPS, otherwise the EPS tends to drink the resin like a sponge and you wind up with a heavy board.
Shaping is done with Electric Planer, Surfoam, sandpaper, dragon skin (sheetrock screen) and also small handheld hotwire devices.
Good luck Chris - be sure to post up pic's of the build.