I am a propestive student of the University of St Andrews as well. I do not how is to live in the halls, I have applied for familie accomodation because I am going with my son.
However, I advise you to start looking for accomodation asap, as the demand in the area is too higher and expensive. The University only garantee accomodation for entry undergraduate students in the halls, therefore there is not garantee that you will get a place. For me is the same, they have family accomodation but they do not garantee that I will get one so the Accomodation Team advised me to look for private rent. I have been looking for since earlier March and I still have't found anything, it is an absolute nightmare. I will have to decline my offer is I can not handle to find something. Your situation is possibly better as in bad situation you at least have the option of renting a bedroom which would be easier. But I have been spoken with staff of the university and students and all of them have telling me that the situation with accomodation in the zone is really bad, many students are living in Dundee because they could not find anything closer. So I would recommend you to start looking, and if they give you a place in the halls, which I suppose you will know during the next month, you can always change.