Piecing stuff together off of ebay is hard.

what controller are you using, and how much current does it draw? It should say in your specs or on the controller. 15 amps isn't a lot for a motor, although that is what I use. 48V @ 1000Watts is 20 amps.

that battery is a 1C battery, which really isn't going to cut it for an ebike. Best I can tell, you need a controller that won't draw more than 15 amps (and that is pushing it on this battery).