Anderson connectors are a common choice for electric bicycles.

There aren't many variable ratio motors out there for electric bicycles. There are fairly decent options, but all with higher installation complexity and often with additional complications. I have yet to see a good electric frame mount kit for a regular bicycle that had no special installation quirks and allowed the use of a double or triple crank. Most of the frame mount kits make for good electric motors, but bad bicycles. Its fine if you don't mind installing a proprietary crank system and dealing with reduced gear ranges and such, but I personally find the geared hub motor to be a better happy medium.