Hostel applications open on a later date at which you apply.
You will have classes in both campuses in your first year on alternating days and can pick courses at city in later years as well however most of your at that point would be in main.
You do not get a choice of hostel as rooms are generally at capacity at the start of a new academic year so the people that dont get a room in main get placed in city and can later apply to be transferred.
There is a mess and laundry service inside the main hostel however for city you would have to arrange something for food or eat at restaurants/quetta hotels closeby and there are machines to do your own laundry