I use bicycle inner tubes for gluing on fretboards and binding. It can be a little awkward to pull them tight as you wrap, but it's super effective (not to mention FREE if you have a cycling habit that results in a steady stream of punctured tubes!)
If you're going to use those templates you drew with a router, consider making the template nice and big so you have plenty of room to clamp it to your body and still have clearance for the router (without it hitting the clamps). You can use double-stick tape on smaller templates, but double stick tape sometimes lets go. Routers can be your best friend when building a guitar - I use routers more than any other tool, by a large margin. But if you're new to routers, they can be dangerous both to your person and to your project, and many of the "basics" in terms of using them safely and effectively aren't intuitive. It can be easy to mess up and tear out a chunk of wood. Really, the biggest tip is probably to take small bites. Don't try to route anything in one pass. For a pickup cavity, you will usually start by drilling out the majority of the wood, then using a router with a template to bring it to it's final shape. Even then, the routing should be done in multiple passes - if you've got a cavity that's 5/8" deep, it might be typical to do it in at least 3 or 4 passes. Smaller passes means less workload on the router, which means smaller chip size and significantly reduced chances of tearout. Smaller passes also means less "resistance" and a router that's much easier to control.