Not all your questions are answered on the GM site.
That the motors are not sealed or waterproof.
GM Electric motors are Direct Drive, not internally geared motors.
The number of magnets and poles is not usually useful information
except in small motors (RC or Aircraft)
The wheel motors are 48V. If you want to run 72V then you are
over-driving the equipment. You may be more satisfied with the
non-wheel motors and controllers from the BLDC motor link on
goldenmotor.com.
And the question your friend did not ask, a 72V 12AH battery pack would
way around 60 pounds, not counting any mounting hardware it would require.
Add 15 pounds for a motor, another 5 pounds for wiring and crap, and you are
adding about 80 pounds to a 20 pound bike.
This hundred pounds would not be nimble, and would probably not be within
the static load limits for most bike frames.
(Remember, the battery, motor, etc are not on a cushy seat and can't stand
up when you hit bumps.)
I am currently running a 36V bike, and after trying Sealed LeadAcid batteries,
I ponied up the bucks for a LiFePO4 20AH pack.
When I get the 48V Magic Pie motor I just received on a bike, I am not gonna
put 45 pounds of lead on it, I am going to bite the bullet and get
the GM pack.
GM: PS: I want a 20AH pack in a nice case like the 12AH ones are in.