i think that a safe amount of players is 12.
this is so you dont pay to much salary (so you can afford a decent doctor)
and you have back ups and reserves.
5 starters
5 backups, 1 for each position
2 reserves, who can play multiple positions
Injuries happen, sometime at the worst times, but it happens to everyone, all you can do is be prepared when it does happen
IE. doctor and reserves.