No, unfortunately the initial tuition and application fees can only be paid through Flywire.
According to its availability, it is possible to change from a single to a double room or vice versa. However, please be mindful that rooms are especially assigned by the housing office and cannot be changed arbitrarily. After check-in, you cannot change the type of room you have been assigned.
Yes, all dormitory buildings have an elevator.
Yes, there is air conditioning in all of the dormitories.