Rose is rumored to be coming back, but she'll be along with Tennant, and they'll have their own way of barging into the story.
That isn't a rumour, that is confirmed for the Special. However that is for the special, so unless this series bleeds into that - unlikely.
I watched The Nerdist later yesterday evening, and in his interview Matt Smith seemed to hint that everything was "leading up to the 50th." So it's quite possible that the anniversary will indeed play some part in the main season.
Who knows, though?
As for the girl in the shop, I don't know.
Could be River, though that's too easy.
Could be Sally Sparrow, which I think would be awesome (and correct me if I'm wrong, but didn't Moffat write "Blink?").
Could be Rose (she has been known to work in a shop, but she's theoretically stuck in Pete's World).
Old Clara and/or some alternate version of Clara? Meh.