I also registered mine as beige/silver until is was painted.
I clipped my front brake lines to the wishbones with a zip tie and some fuel hose like this....
off side - left lock by
marlinpeter, on Flickr
(Note: this pic was taken before all the nut covers, etc were fitted)
I think your vacuum hose should be fine if you clip it where it rubs.
Self centering on the Sportster is a bit odd (due to the steering arm ackerman angles being wrong after shortening the distance to the diff). I found about 2 degrees toe out to work but don't ask me why. Also, pumping your front tyres up to about 35psi helps.
On your radiater cap issue, why not just seal the radiator cap with something like RTV silicone? Any pressure should be taken up by your expansion tank and in extreme cases its pressure cap.
BTW, do you have plans for louvres in your bonnets as I think your engine will get very hot with none in the top or sides?
Don't forget to check the height of your headlamps as its a bit marginal. (just wind up your suspension if too low
)
Good luck and as others have said, take lots of tools and bits and pieces as they will let you fix things on the day.
....Peter