With that much weight, your battery life is what to consider.
While a battery might be rated to provide 30-40 miles per charge, that is
most likely calculated for a bicycle and rider less than 300 lbs., rider at 225
and a bicycle under 75 lbs.
Since it would take a lot of torque(higher torque will result in fast battery
discharge) to drive a vehicle of this weight, I am thinking battery life might
be as low as 5-10 miles per charge(at best).
Add a second rider (even a child under 50lbs) and who know how far a
charge will take you.
Just thinking......
rusty