Hi Richard,
I do not suggest you run 72V, 50V is plenty. Our 9 fet 30A controller, which is a mid-power controller, on 50V will deliver ~1500W input power, and that is at least 1000W plus output power from the motor.72V and 30A is 2160W input power.
A 10T on 50V with 9 or 12 fet controller will top out at about 25mph and have good hill climbing. You don’t want an overly high speed setup if you will be hitting lots of hills. 72V on a 10T is pretty fast and not what I would recommend for pulling some weight up steep hills.
A torque arm and freewheel is a good idea on a rear kit.
The Mac motor uses a screw on freewheel, it cannot use a cassette. The 11T DNP are popular as it allows you to pedal to a higher speed. The Mac can accept a 7 speed without any additional spacers (135mm axle width). If 8, 9 or 10 speed are used, a spacer of ~4mm is required and the axle width will increase to ~139mm. Difference between a Freewheel and a Cassette:
http://sheldonbrown.com/free-k7.html
Drawings for 7, 8 and 9 speed DNP:
http://1drv.ms/QTqx1K
7sp DNP 11T Freewheel
http://em3ev.com/store/index.php?route=product/product&path=41&product_id=63
8sp DNP 11T Freewheel
9sp DNP 11T Freewheel
10sp DNP 11T Freewheel
DNP Extractor Tool
Grin Tech Rev2 Front Torque Arm (forks with eyelets)
Grin Tech Rev3 Front Torque Arm
Grin Tech C-washers
Grin Tech Rev4 Rear Torque Arm
http://em3ev.com/store/index.php?route=product/product&path=41&product_id=88
Torque Arm Info (manufacturers website)
http://www.ebikes.ca/torque_arms/
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Thanks
Paul