Hope you have set the condition type for commission as Accrual and assigned the Accrual Key in pricing procedure. If not, change the configuration accordingly as the commission amounts should not be posted to FI immediately.
Fetching Service Tax and TDS, your pricing procedure should have separate condition types for these two which should be placed below your commission condition type and the From-To step numbers be assigned as that of step number for commission. Coming to approval process, explore the Workflow functionality.
G. Lakshmipathi