The motor kit itself would probably be fine, but the batteries being lead acid are crap. They are much heavier than Lithium.
You wouldn't get very far on 8ah of lead acid, it's not the same as 8ah of lithium, basically from what I know of lead acid is to expect half the capacity and they have maybe 100 charge cycles max. Maybe other lead acid experts would be abale to advise you better.
I still think you are much better off with the 1000 watt geared hub from emissions free.com. better torque for less power.
Check out these batteries http://www.bmsbattery.com/48v/249-48v-1 ... -pack.html
If they are 7 kgs weight like they say, then they are good value for money, but they are not as powerful as the emissions free batteries I don't know if they are reliable, some people on ES have them and they work. The 20ah would give you good range at 20-25 mph.
if getting the bms battery or ping battery You would have to tell cell man to limit your controller to 20 amps or get the program cable and program it yourself to the capability of which battery you get.
The emissions free battery would give you a lot more power for better torque for acceleration and hill climbing but less range
It's all rather complicated choosing the right system.
OH, you need torque arms or plates to stop your axle spinning in the drop outs!
Back to pedal only power.