What sort of tourney are you thinking of playing???
Lost In the woods...
Or Bouncey castle..... whoops sorry Sup Air.
The current legal team sizes for sup-air are
3-man
5-man
7-man
10-man
you need to get enough players to fill at least one of these formats but you will notice if you can find 5 players you have also got a 3 man team.
You also need to find extra players as being a fickle Lot many people decide that they cannot make certain days and thus you will need spares to fill in.
I wouldn't worry to much if they don't turn up on tourney day as at big tourneys there are always pimp ballers that can be convinced to join your team.