“Are we allowed to bring in heaters in to our dorms?”
I am originally from a cold climate (colder than Waterville), and now consider Maine winters to be pretty normal. Therefore I might be biased.
However, in cold climates people heat their buildings well. Also, whoever owns the buildings saves a bundle of money by having the buildings be well insulated and free of drafts. As such typically when you are inside the temperatures will be warm. You are very unlikely to need a heater in your dorm.
You will need good boots, a good coat, a warm hat, and good mittens. All of these can relatively easily be purchased in Maine.
We are from the US but my daughter is currently studying in Canada. As such she has met some international students who are from warm climates. They purchase winter gear, and they get used to it.
There are a few things to be careful about. One is not to try to walk home alone really late at night if you are very, very drunk. I have heard of a few cases of very drunk people falling asleep outside in the coldest part of winter which is a very bad idea. Another is do not kiss or lick metal outside in the winter. Be a bit cautious about slipping on ice. Another common mistake is to take off your gloves and hat when you go inside, and then lose them. If you have a backpack to carry your books or laptop you can throw your gloves and hat into the backpack.
I am pretty sure that you will get used to it. Personally I like the winter. It is one of my favorite parts of the year.