About your question on associating the 4th button. It is really easy. Takes maybe 15 minutes.
Some people might have different methods, but here is what I did.
Made a list of all the neogeo games based on the romname with romlister. Opened up one neogeo game in mame, hit tab, do the game specific buttons, and input your four buttons for neogeo.
Then go to the cfg folder where mame is. You should see the just made cfg file for the game. Then the boring part comes in. I just copied that file like a hundred times. Renamed each one to the neogeo game it would be assigned and changed the system name within the cfg file to match the neogeo rom name. This took 15 minutes tops, even going through 150+, since you just cut and paste. Granted there might be better ways to do this, but I didn't find any right away and this was pretty simple.
It is nice having the 4 button layout, feels real authentic, and on the occasional emulator like snes, you have an extra input.