Can I book a hotel in the shop? Can I pay first and then stay?

Of course, and you just need to find a suitable hotel and make a reservation directly by phone, without paying in advance. Generally, the hotel will reserve a room for you according to your scheduled time after your reservation, and will not cancel it until your scheduled time arrives. However, I suggest you go to the hotel to see the room yourself. After all, your classmates are coming. Look at the room by yourself and feel at ease.