Judging by the replies, 8 function buttons is a bit of overkill.
Normally. (although I don't consider credit and start buttons to be admin buttons, so you really only have 4)
Personally I like having a dedicated exit button rather than having to explain combinations to people. Pause is kind of nice sometimes.
I'd consider having save game and load game if the slot system in mame worked differently.
I still may add it to my cab since it's Neo Geo themed and Neo Geo had a card system for saving games.
Since they're already cut, would volume up and volume down make sense in any of the current locations?
You haven't mentioned what interface you're using, but I know the IPAC can be remapped to post the keyboard volume keys.
There are workarounds if not using an IPAC, as well as it being mappable in MAME.