I can't give you an exact number, because how many pitchers you bring to a game may depend on how your program is structured. When my son played travel at the HS level he played for a fairly well known travel organization. They structured things differently then the normal travel ball program. There were 3 teams at his age level. From week to week you did not know what team you were going to play on. Where you played depended on many factors, mostly you were placed on the team where you would get the most exposure for where you projected to play after HS. For instance if you were projected to be a mid D1 player and a team A was playing an exposure tournament where there would be mostly SEC guys, team B was playing in a local tourney with little exposure and team C was playing a tourney that expected a lot of local colleges you most likely would be sent to team C for the weekend.
Pitchers were part of the pool and where you were assigned depending on exposure needs as well as pitching needs. Figure we would have between 4 and 6 pitchers at a game. If you were at a game it was expected you would get mound time. Sometimes it was only for an inning, but you got mound time. This setup allowed the program to adjust pitching rosters to ensure they had enough pitching to last a weekend. Pitchers basically showed up for their assigned game, did their job and left. You could be playing back to back games with an entirely different pitching staff.
A normal weekend setup would be 9 to 11 position players on a team. Of which 2 or 3 were two way players and would see some mound time. Over the course of the weekend we would see about 12 to 15 pitchers rotate through the team as well. If I were to guess, I would say the average roster worked out like this. 5 strictly position players, 4 two way players, and about 10 pitchers per team.