As an electrical engineer, surely you want to know your instantaneous energy per unit distance, MIN/MAX speed, current, voltage, set cut off voltage/max current and have a PI controller at your disposal for additional control options. You want a Cycle Analyst whether you know it now or not.

And why limit to 36V?

Are you familiar with battery management? Are you planning to balance on charge? How will you know when to stop using the motor without damaging the battery pack? Rather than dumb systems with no monitoring on the bike or during charge, build a system that you can measure battery performance (as with a CA and a charger that measures things like mAh in, internal impedance and maybe even has a computer interface so you can see the voltage profile and state of balance on charge). The CA was designed by an engineer (Justin). Nothing compares to it in capability. Check out the latest info on it at ebikes.ca. He is even working on a PWM I/F to work directly with R/C controllers...