I am assuming you are talking about forming a team for the purpose of competing. If you just want a "team" for the purpose of playing paintball for fun, without entering competitions, then you can have as many as you want, or as few.
You guys need to figure out what tournaments are held near you, how many players are allowed per roster, how many on the field at once, and what the rules are. For example, are rt triggers even permitted? Then you can either enter one and away you go, or watch one and get a sense of what you are getting yourselves into. It is far more common to join a team, when you are new to it all, rather than form a team from scratch, without any "elders" there for guidance. This will mean that you have your work cut out for you... but it isn't impossible.
