Long jumper wires, how big of an issue?

It all depends on what kind of motion sensor you're using - but most reasonable ways to sense a goal won't care. If you were trying to do digital comms over that distance, you might need to think about it, but I get the idea that you're just doing something that'll pulse a pin when it seems something - that'll be no problem. SPI or I2C over that distance would probably work, but you'd have to start thinking about it.

Yes, you can do POST requests, no problem: http://www.espruino.com/Reference#l_http­_request