The buttons you would have would be all the 4 face buttons, 2 shoulders, 2 triggers, and start an back. You could have the face buttons and triggers be your 6, left and right shoulders can be coin and start, then you can auto hot key the select and back buttons to be whatever you want, so you could have up to 4 admin buttons. Use them as select and start on rmulators and then use autohotkey to make pressing them both esc.
What front end are you going to use? I know gameex has built in support to automap exit keys for emus. Makes it pretty easy