Regarding top speed, A motor's max RPM (at least in this setting) is a function of how it's wound and the voltage you supply. A controller can limit it below this, but you can't keep the same top speed with a lower voltage by changing the controller. Amps x volts gives you your torque / acceleration, while volts and RPM are directly correlated. I just had a custom 20" wheel built for my trike, and I needed to have a custom motor wound for it to get higher RPM at the same volts. Rather than ~240RPM, I had it wound for 400RPM to maintain approximately (slightly higher) top speed with the smaller diameter wheel. The downside to this is that you get less torque with a higher RPM - basically like gearing in a transmission, except it's baked into the motor itself.
For charging, I bought this 36v 2amp power supply:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Snipped the ends, replaced it with butt-ends and made a butt-end to XT60 adapter.
