Thomas, it isn't difficult for Zarra to follow Perry. She is a trained drow rogue and he isn't trying to be stealthy or anything. If you, or anyone else, follows him you will find him heading to his room.
Regarding moving on, I believe we are currently in two separate timelines here and this situation is taking place the night before we went looking for mercenaries in Baldur’s Gate. Velon stated on page 948 in his post, “Velon addresses the group over yet another meal in the castle after the interrogation of Varram.”
So in “the present” we (I.e. Lia, Perry, Tazskan, and Zarra) are still deciding on hiring captain Callahan as mercenary captain. Velon and Lawrance are back at the castle. Poljen and Nikolaos are off doing recon/spying. Once we decide on hiring the captain and Poljen/Niko are finished, we can head to Candlekeep.
EDIT I also don't mind taking the Perry subplot to side stories so we can all stay on the same timeline in the Main Thread.