From 2 years of experience of coaching 9 a-side football, I'd probably go with;

1 Goalkeeper

3 Defenders

1 Deep-lying Midfielder

2 Wingers

1 Attacking Midfielder

1 Striker

Having 3 defenders at the back should be safe enough, I've found, as most have 1 striker, quite a few had 2, but with your deep-lying midfielder, you've always got cover at the back if the 3 are struggling. You'll just need tomake sure your deep-lying midfielder is a good passer, and has good stamina, as he'll be focusing mainly on distribution after receiving it from his defenders, or the wingers. I found, with our squad, we only needed one striker as the forward we had was brilliant at linking up with the attacking central midfielder, aswell as having the power and pace to make bursting runs through the gaps in defence.