For Folks new to bikes with motors
First off, welcome! This is an exciting, fun hobby and a great and economical form of transportation. The forum here is a wealth of knowledge and fine people who love to help, just ask!
I just looked at 2 new dealer's web sites and just wanted to offer my opinion on some things and folks here will either back me up or correct me. All about the "one for all" thing
There are no 80cc china girl kits (AKA, happytime or HT) they are smaller and varied. There are better alternatives to drilling your frame when the front mount of your engine does not fit the down tube of your bike. I have never got 150 MPG on any build and I way 165 LBS and live in a very flat area. Normally around 130 MPG. I have yet to meet any one who on their first build, did it in 3 or 4 hours. I strongly suggest you build slow, right and tight. I hazard to suggest, enjoy that part, is very soothing and gives you time to get to know each other.
There are a bunch more, but I digress to those who know better then I. In closing, I suggest you get what you really want by doing research and getting more then one opinion, most especially mine.
I look forward to the pics you post of your creation!