How to hook up a mains voltage relay?
Screw terminals like you show are a very bad idea for dangerous voltages unless the whole assembly is normally covered with something not easily removed, like a electrical box.  The screws at the top of the screw terminals will be connected to their line.  It would be too easy to accidentally brush up against them.

Your ultimate 500W load will draw nearly 5A, so make sure all paths of that circuit can handle that.  I see the relays are rated for it, but what about the PCB traces between the relays and the screw terminals?  If you are buying this board as a unit, check its ratings.  Don't assume the whole board is rated for 10A just because the relays are.