My two cents...
I'd rate your guards in this order:
PG skills: Hatch, Baker/Lanier, Sullivan
Offense: Hatch, Baker/Lanier, Sullivan
Defense: Sullivan, Baker/Hatch, Lanier
So I think Hatch should start at PG. Sullivan either (a) starts at SG if your opponent has a good scorer there or (b) backs up Hatch at PG if the opposing SG doesn't put up many points and the opponent doesn't run press. If (a), then Baker backs up Sullivan at SG and Lanier backs up Hatch at PG. If (b), then start Baker at SG and back him up with Lanier (equivalent offensively but Baker is better defensively.
At SF, I'd rotate Cespedes and Renner. Cespedes is the better offensive player and rebounder, Renner is the better defender. Start one of them based on opponent's strengths, back him up with the other.
I'd start Arrington and Beamon as the bigs. Arrington is better offensively, Beamon the better defender; who starts where would be contingent on the opponent. Start Arrington against the weaker defender and start Beamon against the better scorer. Back up Arrington with Harris and back up Beamon with Grier. Schulman is only a freshman, he can live on garbage minutes this season; he is your weakest big man and shouldn't play meaningful minutes.
I am a big believer in moving guys around based on opponent, as you can probably tell here!