when I hook up my power socket, is it going to be best to wire up to the existing accessory socket, or can I hook up to a nearer power source without hacking into the loom too much?
BM do a accessory socket add on. Just unplug the plug on the back of the current external socket, and it just plugs in in parallel. Dead easy and you can move it around bikes if / when you sell it as long as you don't hack any holes in anything.
BTW there was a change in about 2005 for the plug type