I have a front wheel hub motor. Anyway, you'll have to wire it yourself so I wouldn't buy any wire online, I'd but it at a hardware store near you. I went to Lowes or Home Depot and they have these spools of wire and you just tell them how much you want. I told them I wanted 20 ft of 10 gauge wire. It was about $12.
For the charger, I bought a 12v black and decker with 2/10/15 amp selection capability so I can charge at 2 amps or 10 amps. This is good because you have a 20 AH battery so you'll need more than 2 amps sometimes to charge it. Just don't use over about 10 amp to charge.
I would get the one that has a 2/6/10 amp because 6 amp charging is better than 10 amp on the battery. They say 6 amp is the optimal charging current for these 20 AH Thundersky so I'm using a little over it but not by much. Sometimes you'll only use about 4 AH on the battery and then you can use the 2 amp charge. That's what I do. A 12v charger is good because if you upgrade, you can still use that charger. If you buy a 36v charger and then upgrade, you'll still need another charger for that 4th pack.