good advise about doing title first before dropping a dime on it.Since by the letter of the law you can't plate that bike, I would not spend anything on things like wheels until after you get the plate. You might slip by and get a plate but it would really suck to spend $2k and not get a plate. Street reg first and goodies later.
I would get the lighting coil that you can get from Ricky stator. It's not very powerful, but since you must have a headlight on the street it's pretty much required. It will run a 35watt headlight and tail/signals.
A KX with the more or less MX style transmission will need to be geared out to go high speeds at reasonable revs.
www.supermotojunkie.com is a really good Supermoto site.