Hello and yay for Cornell!!
What department are you in? Depending on where your classes/work will be, where you should live to avoid the big hills will be different. However, as my friends and I used to joke about in undergrad - at Cornell you walk uphill in the snow both ways to get to/from class. It usually isnt possible to avoid all hills. Motorists are pretty good on campus, because they know students are likely to jump into the streets at any time to cross, and the roads will be fine in the summer and part of the fall, but I really would not recommend relying on a bike the full year. While the streets are well plowed in the winter, there is always some slush and often poor visibility so I would consider it too dangerous to ride during those months.
If you are looking at lower-collegetown, there is a very decent bus system (tcatbus.com) that could be used when the weather gets bad.