Hi Ted -
Found any answers since you first posted.
(Belated welcome to the forum, btw. Just came across your post.)
Your extremely modest range & top speed requirements are a good thing, both from the point of view of keeping costs down, because you won't need a really powerful motor, and also from the point of view of having a manageable battery pack size.
You didn't mention what kind of budget you're working with though...
Which makes me wonder if you're up for going with a lithium battery pack. Since you don't need a pile of capacity, you may be able to set one up that's not horribly expensive.
2 pieces of advice:
1. Spend some time on the EV Album if you haven't already. Look at what other 2-wheel conversions have used.
EV Photo Album: Our Electric Cars on the Web
2. Vancouver has an EV association with regular meetings. I expect you could learn a LOT by attending a meeting or two and letting people there know what you're up to. EV aficionados also tend to have spare parts and expertise that they're willing to pass along.