Acceptable for Steam or modern console fighters IMO.
I did 7, but on a newer steam fighter it required mapping 8 action buttons to exit the remap screen. I had to open the control panel and jumper some contacts to get through it.
The default mapping for MAME assumes you have 6 buttons like so:
123
456
So do it like this and you'll have a lot less remapping to do in MAME:
1237
4568
Stick to this and the only games you'll have to remap are the Midway fighters (Mortal Kombat series, War Gods, Mace)
I also ended up using #7 as a dedicated "Tag" button on all games with a tag team feature.
The Neo Geo games end up using the first three in the top row, then #4 in the second row for the last (D) button.
I have a neo geo themed cab which has the "Neo-Geo 4-in-a-row" up top, but found that I prefer hitting the D button with my thumb rather than use my pinky or reach over.
I ended up mapping the D button to both so either can be used.