That bicycle should work fine, however I highly recommend getting a different one that has good direct pull front brake or a disc brake. Remember, if you are moving quickly, you will need to stop quickly too. A coaster type rear brake is not enough in my rule book.
As for an engine, I say get an EZM. There are many members on this forum who are authorized EZM dealers.
Quenton Guenther makes them. As for authorized vendors, scotto- and azbill come to mind first. Sorry to all the others who I cannot recall right now.
Here is EZM's web site:
I have an EZM and so far I love it!
A second choice would be a 4GT system from http://www.bicycle-engines.com/
I have no experience with them, but I have learned that after a few modifications and welding they can be made reliable.
There are plenty of threads on this site that discuss both drive systems.