That should cover you for the buttons used for gameplay. Some people, like me, have 7 action buttons per player in a street fighter / neo geo hybrid, but I never use all 7 buttons on a single game. Others can chime in on this.
Some people have admin buttons for quit and stuff like that. I just have a button for pause on the side of my control panel. If you have an Ultimarc iPac encoder for your controls, you can set up a key as shift (hold it down and press another button for special functions.) My pause key is also my shift button, reducing clutter on my panel. Look at the encoders at Ultimarc.com for more details.
You probably want test and service buttons too, for configuring your games. On a real cabinet, these are inside the coin door. Depending on your build, you might want to put them somewhere (or use the iPac shift method.)
Just to give us an idea of what and where to place buttons, what type of build are you doing? Upright, or Bartop, or other? Using a real coin door? (you can put service, text, and admin buttons in there.) Do you have a way to control volume, or will you need buttons for that too (adjust volume with the PC or using an external volume control?)