I ran 11 in No Quitters and one guy only had 20 innings. He was a setup A though, he just only had 5 STA. I probably could have ran 10. My staff was:

SP #1: 22/99, 263 innings
SP #2: 29/83, 250 innings
SP #3: 26/77, 190 innings
SP/LRa: 24/79, 158 innings
SP/LRa: 26/68, 143 innngs
SP/LRa: 19/80, 125 innings
Mopup: 29/82, 65 innings
Mopup/LRb: 22/79, 69 innings
SetupA: 87/5, 20 innings
SetupB: 49/35, 78 innings
Closer: 42/40, 84 innings

I basically ran a 3-man rotation with SPs 1-3 set to no pitch count. I juggled the other 3 guys between starts and long-relievers. I had 2 guys with decent stamina as mopups or to eat innings in blowout wins/losses.

I could have easily ran a 10-man rotation without the Setup A, and as the Long B guy was often used. As mentioned though, there's kind of no point, because even with all that, I had a bench guy who only got 75 ABs. I don't know what I would have done with another bench guy.

12...

My optimal is 11 and I usually can go 10 but having that many bench players is a bit excessive, as stated above.

I don't worry about my staff's stamina/durability so much but instead like to get the 30-80 guys for the pen.

One exception, my Kenny Powers team, 10 pitchers. But that's like a special circumstances team ;). My staff is exceptional and my hitting is about the worst collection of guys you could throw together. So I figure more hitting and I just go with the hot hitter and get lucky.

depends on the ballpark, the quality of the pitchers, and the DUR/STAM combos, it's definitely possible