I'd second the recommendation to skip the powdercoating; my experience has shown painting is the better solution in this case.
Sounds like a wiring harness or some wiring issue to me. My first step is always shaking, pulling and prodding each set of wires, with the bike ignition on and the battery hooked up. Gently and in some cases a little more forcefully, pull, push, poke and giggle any and every wire and lead you can to see which one, if any, may be shorted out. Take the tank and seat off so you have better access to the harness, starting relay and anything else you can give the ol' pull and prod test. I've had similar issues on older bikes and my theory..."when in doubt...it's the wiring".
I've the same opinion, and in fact have gone to great lengths to find pieces w/ original paint, and, of course, patina. My /5 has factory paint and pinstripes on all of the bodywork and it looks quite nice, if I do say so myself. Yes, there are imperfections and such, but it's a 35 year old motorcycle and should reflect such. My stance on the mechanical side is not quite the same, though; my /5 starts on the first kick or push of the button everytime, as any 35 year old bike should... kix