their should be at least 5 pitchers on a team [5 starters]. But you can have up to 15 pitchers.
Generally there are 12 pitchers on the 40 man roster for a major league team.
4 pitchers * 3 catchers = 12 combinations
There are 30 teams in MLB and each team carries 11 or 12 pitchers. That would make between 330-360 pitchers on active rosters in MLB.
For active players, about 40. (counting pitchers...)
Most teams have 12-13 pitchers on a team. However, in September they are allowed to expanded their rosters from the original 25 to 40; at that time they always include another 5-8 pitchers in the call up.
Pitchers are chosen by the manager of the team
at least 24 including the pitchers and the back-up
There are nine players for each team, but there can be substitutions at any time, particularly for pitchers.