You've decided on a caliber. That's an approach I often suggest to folks, since the bullet is the weapon that acts on the target, not the launch platform. Pick the caliber based on the job you want to do.
However, I'm curious, how did you decide/what was the thought process in selecting the capacity?
Eh, just mostly what was available in the caliber within the weight restrictions, from what I found in single stack you're going to get 6 or 7 and that depends on the size of the weapon and if its an extended or standard magazine. I guess posting capacity was pointless but I would have preferred having 7, but I want to stay with 9mm and keep the gun as easy to conceal as possible. I guess when it came down to it I was comparing say Kel Tec's standard 7 round PF-9 mag to the kahr pm/cm9 standard mag of 6, while still being lighter and yet there's the MP Shield with a standard 7 round mag or an extended 8 round mag and its heavier.
So after weighing everything in...I feel like the CM9 is a good compromise. Who knows, I may buy it, hate it, sell it, and start over. I'll let you know!