Quick disconnects? If you use them it means less soldering and you can easily switch around wires and buttons. Im not sure what size you would need, never used happs and not sure on the lug size but im sure you could check lizardlick for the size. Of course quick disconnects arent essential, you can solder straight to the button.
You may want to use a terminal strip as well to keep everything tidy. It also means that if you mess up a wire its simple to swap and change what is going to the button on the other end.
Grab yourself about 4 ft of cat5/6 cable from the home depot, they can cut it right off the roll and its dirt cheap (it’s 24awg and the cat6 is stranded so it bends just right). skip the kit if your just building 1 and just grab a gun, solder, and flux from radio shack (dont skimp on the flux, it’ll save your tips)