As Phil said, 18ga is overkill for the feeders attached to the track. You'll probably want either 22ga or 24ga solid wire for that. In two colors - white/black white/red or red/black which you then tie to the 18ga bus. If you use some sort of terminal block you can always replace the 18ga with 16ga if you find out you fail the "quarter test" and need a heavier bus wire. Or if you solder, just snip the feeder off at the joint and re-wire. For free it might be worthwhile to try. Although for a HCD the few feet of 16ga wire won't be too pricy anyway.