Well, for the switches, they'll only use a very small amount of power, probably no more than a couple hundred milli-amps during the switching, and a fraction of that just lighting the LED's. So, strictly for the switches, almost any size wire would work fine. As far as the accessories, it really depends on the current draw of the lights and any other electrical parts.
I'd expect that #18 would probably do the trick for all pretty easily.
