Having been foster parents, I will have to say that this is so situation dependent that I would have to caution you to see how thing settle. One foster was of the "you aren't my parents and can't tell me what to do" mode. That lasted until a case worked explained that she could stay with us and obey the house rules and orders or go back to the group home. She though about that for a little while and decided she liked having a bedroom. It was kind of funny actually. She would start to put the brakes on every once and a while and my wife would give her "The LOOK" and instantly the situation was resolved.
I wish you luck and good times.
Matt