You should also get a digital multi-meter, for testing voltage drop, determining amp flow, etc. I got mine at radio shack for $30, and it worked just fine.
Oh, and do all the work without the boat batteries on board, and not hooked up to shore. I used a couple of 6 volt batteries in series to get a small-amp 12 volt for testing connections. Large enough current to get the lights on, but not so strong as to give me a nasty shock or cause a fire quickly. Be sure to leave the batteries unconnected.
I'd suggest you get a whole new electrical panel, which is expensive and a lot of work, but in the end, you'll end up knowing what each and every wire is.
IF you're going to do the AC, you should replace the circuit breaker box under the cockpit coaming with a plastic box, and perhaps add a galvanic isolator. Additionally, you should separate the AC terminal block from the DC terminal block, for safety reasons (both are located in the small space under the nav table storage area).