Hi well here goes "opinions" I use Worksman wheel sets, Sturmey Archer Wheelsets, and the least expensive I use are .105 steel-spoked chrome wheels from Taiwan.
For an engine kit I would choose either Whizzer (not real easy to find) or EZ Motorbike (availble all over).
I like the old 2-bar frames and an in-frame tank would be cool, I would also look inot some kind of suspension for the front. American made Schwinn springers can be very good, as well as Cleveland Welding and a few other companies.
you can see some of those things here
Simpson Motor Bikes
Mike