If I were to build another one, it would be a 24-26" bike with a rear wheel hub motor. There are lots of affordable e-bike kits on ebay rated up to 1000W. The main reason for RWD is I'd definitely want a full suspension. And btw, some of those kits come with pedal input sensor, similar to BionX system. For fraction of the cost in the links above you could build a very capable machine.