[dtbaker]

... I was thinking (with no real basis for it) that a 72V 100AH system would be good.

this will be very sluggish..... and prone to holding up traffic.

I would suggest a minimum of 120v - 100ah lifepo4 (thundersky or calb) with a 9"dc, or 8" at very minimum with cost effective 400-500amp controller like the curtis 1221 or 1231.