I always like to use 250w-350w motors because I don't need speed or power..
I always like as much distance..
I'm in south florida so it's all flat around here. If you live in a slightly hilly area, go with 500-750w motors.
If you live in very hilly areas, then an 800w+ motor is for you.

Just about any motor will do for me because I only run 250w-350w continuous and most motors handle that easily.
36v IMO is the best for price per weight.
Smaller wheels provide more torque and more speed compared to larger wheels...

I use Goldenmotor controllers, they run voltages 24-60v and when used with 24/36v they only pull 25a max. They have regen, cruise control, reverse, programable, alarm, horn, etc, etc all in one controller