@Kris92
You should have a different set of rules and expectations for long-term guests based on what you are comfortable with. @Kelly149 makes a really good point about not discounting too much - make sure you factor in a very generous level of utilities payment and emergency budget for a few small things. I'm sure you will have a good idea what people would pay as monthly rent+utilities or what it would cost to stay at a local motel for a whole month. Price yourself accordingly - you are providing a fully furnished, utilities included place.
And especially if it is a private home listing providing weekly sheet changes or soap/shampoo top ups or just very basic vacuum of living room&kitchen areas is a great way to check-up on the guest (and you should mention this is non-negotiable). IMO if it were me, some of my biggest concerns would be long-term guests wasting utilities that double my bills or bringing friends or people over (guests of the guest) and letting this endless flow of friends come over to do laundry (at my expense) or have huge parties - I hope you have outdoor surveillance of the front entrance. Also, if some of these students are coming back next semester, they would have intimate knowledge of the entry points and layout of your home, and might be able to make copies of keys or even make copies and give them to friends etc. This last point is actually one of the reasons why I refuse to host locals - too risky and a huge safety concern.