Help for ESC available in the Shop !

Hey, Im not answering this officially, just trying to help

It looks like they are Emax ESCs...
Yes they do have BECs.
Not really its more redundant to use all four, since its your first build I wouldn't muck around with the electronics too much.
Again, don't worry about it since the extra wires will weigh virtually nothing on a quad this big.
A UBEC is a Universal BEC. Its just an isolating circuit for generic purposes.

Yes ESCs are generally compatible with every flight controller available however whether or not your configurations are compatible is something you will have to pay attention to.

Hope this helps,
Mike