The lazy answer is to refer you to Bob Nuckols book (
www.aeroelectric.com).
Good places to get electrical parts is B&C Specialities, Steinair and ACS. A local boat shop might have things that you need, too, such as West Marine. Also, check out Digikey for switches and connectors.
You can put off wiring until fairly late. If you add the plastic conduit in your wings, you can easily push through wire after you mate the wings to the fuselage. Running wires for a wing-mounted servo now might be a good idea, and that is what I did.
A lot of people don't do local grounds - they bring the returns back to the central ground. I think local grounding of non-pulsed things such as nav and landing lamps is fine, but not things like strobes or magnometers. If you do local grounding, just make sure the electrical path back to the central ground is well bonded.