[elhigh]

I can see you're enthusiastic about the project, but it looks like you haven't had a lot of experience in the field, yet. So here's my suggestion:

Build a go-cart instead.

It isn't that hard to find a frame. If you're even a lousy welder, you can make one that'll work well enough to hold your weight and bear the stresses of the drivetrain. You'll also have a lot more room for mounting stuff: batteries, motor and the like.

Why a go-cart? Well first of all, you can't title and register it for street use. No way. So there's that stressful process eliminated from consideration. Build it well enough to haul you around, preferably in a hair-raising and entertaining fashion, learn a lot of stuff along the way, and most important, this gives you the opportunity to, while you're at it, meet a lot of people who've done this kind of thing already and can give advice both on this project, and on the next one - the one you DO want to ride on the street. When it comes time for that project, you've already gotten your hand in, have experienced acquaintances who know your name and what you're about, and only have the untested waters of titling and licensing to go through.

When it comes time to retire the go-cart, you will probably be able to reuse lots of pieces: the motor, controller, batteries will all be small form-factor models, since even though we're talking about a go-cart, it's still a lot tighter a fit than, say, a Geo Metro. So fitting componentry will be something you've already got a little bit of experience in. The weight of the go-cart will be comparable to a full-up scooter - unless you go with a big cart, in which case you'll be shedding lots of pounds with the scooter. The motor, if you can reuse it, will be all the power you could hope for.

I'm not an EV builder, but I've been reading every EV publication I could get my hands on for about the last 30 years. So my recommendations, while untried, aren't completely ignorant.

Etek motor if you can find it. They're fantastic motors. Pricey, but worth the investment.
See the EV section in this forum for more info on PWM motor controllers. You may be able to roll your own.
Sealed LA batteries, for ease of installation. Wherever they fit, whatever direction, sealed LA lets you get away with it. Mostly.
48-60 volts is lots and lots of speed with a small vehicle and an Etek. Warning: you might kill yourself. Just so you know.