Hi,
Its always good to intro yourself first on here...
As to the bike, it depends what you want it for...
cruiser bikes are good although I have yet to see a full-sus one of those...
MTBs are also good but there can be issues with things such as the rear suspension and the disc brakes and such...
Pretty much any bike can be motored, its just a matter of how much you are willing to do and/or make to get the thing to work...
good luck with your build
Jemma xx