I've done quite a few of these..
I've used this same motor over-volted to 60v and a lighter "mini-bike" (Razor Mx-500) with full suspension. If you're going to use this mini-bike as a frame, I think you'll need a bigger motor.
With the set-up mentioned above I got up to 28 mph. In your bike plan I think you'd probably get 15 mph max out of it. A razor Mx-650 will do that in stock form and costs less than the mini-bike you are planning to buy.
Try this motor with that frame:
http://www.robotmarketplace.com/products/NPC-4200.html
You'll also find a suitable controller at that website.
For the 750-watt stuff and a nice controller, go to TNCscooters.com , they have the best deals around. They also offer 1200-watt motors.. Good luck!