neo geo uses an 8 way stick, so your safe with that. both 8 and 4 way sticks use 4 switches its the opening that the stick goes thru that determines which it is, so wiring them up is exactly the same. as far as using another 15 pin connector to sire your own controller you can totally do that and it is as easy and it looks. just make sure to wire the switches to the right place, use crimp-on quick connects so you can move the wires around if needed.
good luck