Last year Pierec played 66% of the team's SF minutes and 4% of the teams SG minutes, let's assume they keep him exclusively at SF. That leaves 34% of the team's SF minutes to be played. However Posey only played 19% of the minutes at SF, with the remaining 15% going to Ray Allen (9%), Brian Scalabrine (2%), Tony Allen (1%), and others.
Let's assume Pierce is used exclusively at SF, since they have Tony and House playing bigger roles at the guard spots. That leaves 30% of the SF minutes. Give Tony Allen - Ray's minutes and his own for another 10%. Now you basically have Posey's 20% left. I suspect they will hand these out to Tony Allen and Scal as a platoon. Scal will get a shot at the bigger guys and Tony will take the smaller guys.
Giddens and Walker are likely uncounted on for now. Assume they are signed, they may break in like BBD did, or they may ride the bench and see the NBADL like Pruitt.