Easy - get some people, make sure you have gear and call yourselves a team
Other than that, what do you want the team to do?
To play tournaments you need the minimum number of people
Ideally more than that to give yourselves extras because not everyone is going to make every date in a league for a year, add some pit crew to aid your reloading, cleaning off, and herding you all making sure you're ready for the next game
A good organiser is ideal in your pit crew, hand them cash in the morning and they make sure it's all there to pay for fees and paint
For scenario etc a team can be anything, two people are a team
Finally - what is the purpose of the team, what commitment do you want etc
Are you highly serious, or a bunch of guys just out for a laugh