Your proposed build is really similar to mine, except that I used a road bike. And your commute is very similar to mine. I do 12.5 miles each way to work and back, with a couple climbs a few hundred feet high--one just under five hundred. Here is what mine currently looks like, except that I have done some wiretucking to improve the look a little.
http://ecomodder.com/forum/showthrea...tml#post542573
I have the front hub motor totally independent of the rear pedal hub, for simplicity, lower cost, and flexibility. Yesterday I took it 21 miles and did very little motor. Sometimes I am nearly all motor.
My battery was initially above the rear wheel too. Not a great location. I moved it to the triangle for less rattle and MUCH better manuverability.
Also seek puncture resistant tubes, tires. Necessary because of all the weight and miles and heavier use of roads dominated by cars and trucks with their sharp debris.
I LOVE IT. Nearly 4800 miles on it now.