MinnFlyer has it down pat. From practical experience I can not comment on the GP hinge cutter. I only read somewhere that it CAN (?), be a handful till you get it mastered. I would experiment on scrap first till you feel confident using it. I personally use the Harry Higgley hinge cutting tool. It worked great for me. Yes.... bar sanders a must. I save a lot of the light ply after punching out the parts. (pack rat) One thing you can make with these is small "sanding sticks".. Maybe 5 or 6" long and a few narrow ones up to 1" or so wide. I buy the stick on sandpaper from GP and just stick it to the ply and trim with a razor blade. ( you might want to spray some clear coat or make sure all dust is off stick so the paper sticks weel). I use a razor saw a lot. Trimming off servo arms, plastic control rods tubes, etc. Cutting thick balsa is very easy with a razor saw. I don't know what you will end up with for a building board but here is a hint if you use a ceiling tile. I "thought" my new work bench top was very level. I put down the ceiling tile and layed a 4 foot straight edge at several angles and found it had several low spots that ALSO showed up low in the same areas on my bare work top too. I got a stack of index cards, and started putting 3 or 4, (or more), in small stacks under the tile till it was perfectly level. In case I needed to lift the tile ..... I ran a long piece of scotch tape across all the cards to lightly secure them.
Good luck on your project..... lownslo