Purchase order release workflow rule

Hi ,

I have made a zcopy of standard workflow(WS20000075) for PO release. My requirement is that there are three level of approvers who have to release the PO. MM consultant says he will assign the approvers for all three levels from SPRO. As per the std workflow there is only one level of approval as far as i have understood .every time if approver rejects the po the mail should go to outlook also , to initiator and the next approver . 

standard rule 20000027 is taken care for all three levels of approvals ..what is the binding for rule to workflow?

from workflow side what are the customize things should i follow..i am new to this MM workflow can u please guide me ..

thanks,

sandeep chennoju .