Well First
You need figure out how much you want to spend on this project..
Then see what your kit options are in that price range.
Then decide how important reliabilty is to you.
Are you just looking for a bike to cruse around on once and a while ??
Or is it going to be a main source of transportation ??
Are you good with tool's and mech. stuff ??
kinda gotta answer some questions then start reading up ...
There are some m/b's videos on youtube that can give you some ideas on how the different kit's work, Friction, belt, chain etc....
When your ready to buy remember whatever you buy sooner or later your gonna need some spare parts !!!! So it would be a good idea to buy from a place that will be able to help you in the future....
Good Luck !!!