how to setup the Org str to implement bid invitation and response?

hi everyone:

There are some problems that puzzle me for a long time .

1. Operation Purchaser create a bid invitation in SRM portal . And now the status of the bid is waiting for being approved. I think it is the duty of purchaser

manager to approve the bid invitation. but I do not know what role i should assign to the purchaser manager? it is the same as purchaser?

2. where should I put the bidder , purchaser ,purchaser manager in the Organization Structure ? that is the screenshot of my Org Str . Can you give a advice ?

3. Are there attributes that i should maintain? I have maintained some attributes , but i do not know it is enough .

Regards

Charles