0CP Field Defenses
0CP Elite Rifleman
3CP Flamethrowers
6CP White Phosphorous barrage
8CP M10 Tank destroyer
17CP combo
CP limitation is a bad idea. It's not about power rather than timing.
And honestly, I don't think this would be OP. We already have Elite Rifle
But second option is to give each ability status, like basic, uncommon, rare, super rare etc.
In that case you could use 2 rare per commander or 1 super rare.
The only thing is, which abilities should be rare.