If you were in the NL (so no DH) and you were trying to create a bullpen-style pitching staff could you get away with carrying 14 pitchers? Or is carrying 13 better?

I was thinking 8 starters, a backup catcher, a backup high fielding guy, and a backup low fielding guy probably wouldn't be enough...

If you only have 11 position players, your 3-4 lowest durability starters are going to run into fatigue issues towards the end of the season. Only having 2 backup players for 7 positions (not counting catcher) is usually not enough to keep all your starters at 100%. I would recommend 13 pitchers and 12 positions players.

You should also consider PH duty in the NL. If you're trailing, your 3 bench guys are bad PH candidates. Also, you've got limited replacements if one of your starting 8 gets injured.

Bullpenning is tough to do at the major-league level. Easier in minors as you can have a slew of inactive pitchers to activate when needed. Also, you run into demotion penalties if you do as real-life MLB teams do an yo-yo players back-and-forth from the majors to AAA. As dyounquist and outlaw have pointed out, you will run into durability issues with your position players. You might be able to use two spots in your rotation as openers, but that would be it. You need to have 13 position players.

I've run 13 pitchers with no problem. 14 seems like a little too much.

I typically play in pitchers' parks, so I can easily go with 10 to 12 pitchers. I'd rather have the bench guys for defensive subs and pinch hitters.

I have not run a bullpen style staff but a couple of team in my league have successfully done it. The key seems to be they have quite a few guys that can get you 100+ innings a year. It doesn't seem like the key is adding pitchers to cover the innings. One team in particular usually would have 8-9 guys with 100-200 innings with 7-8 between 100-150. You need to have bats on the bench to pinch hit/double switches etch.

Count the innings. Look at past year's IP. Or, if you have young players, look at similar players past IP and see how many IP a player has each season. If you get get your staff up to 1500 IP, you should be in good shape, the better and less amount of pitchers it takes to get to this number of IP, the better and more versatile your lineup can be.

I always run 13 fielders and 12 pitchers. 4 SPs with a spot starter, 3 LRs and 4 SU types, one of which may be a closer if his stamina is really low. I prefer having the extra player off the bench for PH and Defensive replacement options.