Re: Vintage Schwinn or 70's Free Spirit?
The white bike has a suitable frame for a china kit, but those thin rims won't hold up well to motor power. They can be great bikes, but a mountain bike would probably be a better first build due to heavier rims and tires. Look for something with V-brakes at least, a steel frame shaped like your white bike, and decent components.
Schwinn, GT, Diamondback, specialized, all made good mid-range mountain bikes in the late 80's early 90's that can be found at good prices now.
Your free spirit will work, but is not a great platform for a motor.
Your schwinn is the wrong kind of frame for a bolt in kit due to the low top bar....
It CAN be used, but requires major modification to work.
If more is better, then too much is just enough.
If you can't afford it, build it yourself.