for that I used 5mm fiberglass. Basically there is two layers on each side of the wheel and sometimes even more when holding the ball bearings.
The 10mm main shaft is part of a T-Rex 600 R/C Helicopter as well as the matching one-way bearing.
Actually I had to use two one-way bearings. The one holding the main gear is from the T-Rex 600 and the one which is connected to the wheel is from a T-Rex 500. That's also the weakest part of the whole design and I have to change it from time to time.
Motor is Scorpion HK-4025-630KV
I tried various main gear types but finally came up with an "arrow-shaped" one from a Mikado/Logo Helicopter which gives low noise and good strength.
For the Electronic Speed Controller you can choose whatever matches your motor's requirements.
In my case it's a simple 85A, 2-6S piece from HK - costs around 35$.
4S (14.8V) LiPo with 10 Ah.
I would say that's enough to cover distance of about 10km. So in my case I usually recharge twice a week.
Just google for "thumb throttle"... and do the same to find one of these "servo testers" - no big deal.
There isn't really any - just the original one you stomp with your feet.
So be careful and look ahead ;-)