Welcome jcr I'm kinda a noob here myself. I think you did the right thing to look before you leap and based on my time here and reading/research you couldn't do any better.
I'd ask you how much of a mechanic you are, what kind of tools & shop you have to work within, and if there are supply places around where you live to
get things you need to complete a project. If that's available then you could
go with a kit for the first experience. Everything will be there for a bolt on and you should have a good first successful experience. Riding to work and for errands could save you money for a real home built of your own for the second bike. (if you even want to)
But check out the friction drives that mount over the front wheel, the inframe chain drives, and the rear friction drive weed whacker contraptions.
Do remember that the state you live in has laws regarding the displacement, HP, and equipment required on your bike not to mention license and insurance.
In Ohio where I'm at your bike has to have pedals and operate within three feet of the edge of the road at no more than 20mph. Every state is different
so check out the links posted here for the laws of your area. It may drive your purchasing decision. My 30+cc 0.8 HP "helper motor" friction drive system should get me along at about 200+ miles per gallon and for now that's enough for me. (see my "Eureka I Found It !" thread) this may be the research you're looking for.
Welcome and good luck !