Tighten the numbers early on, that will give you an early pointer as to whom can fulfill the charter requirements. What sport is it? That too may have an impact on the type of suitable aircraft, do you need to take you’re own equipment, or can it be rented/bought at location? Depending on the size of the athletes (eg Rugby) that too can have an effect on the type of aircraft suitable for the charter. If there’s five of you and you don’t need lots of ‘stuff’ then that potentially opens up B200 King Air type aircraft too.
How long are you going for? That will determine if the aircraft and crew ‘stay’ with you or get used between flights.
There’s quite a few variables as you can see, the best thing is to determine how many are serious about going and what stuff you need to take, and how long you’re going for. Having tried a similar thing as spectators a few years back, many will say yep I’ll go, when it comes to nailing wallets to the table, the tumbleweed factor may apply!