there is no event triggered by visiting all the dorms (at least not that i remember). The swimsuit section is the most annoying part in Act 1. You first have to grab Hermione's favourite swimsuit, then you need to steal a swimsuit from each girl (doesn't matter if it's their favourite or not). After you've given each girls swimsuit to the sorting hat, you need to go to the sorting hat and ask him to create different versions of Hermione's favourite swimsuit for each of the other girls. Once that's done, you place the girls respective version of hermione's swimsuit on their laundry line, you also need to steal each girls favourite swimsuit. Remember you need to do this in one in=game week. Refer to your journal's note section for which swimsuit appears on which day. Refer to the google document for a more extensive guide.