Ask 1000 people and you'll get 900 different answers. Personally, I've lived on a Cal 27 for 6 months so far in the Great Lakes and it's more than enough space for me. Nothing is perfect, but I gaurantee it beats the hell out of a van in comfort and space. I have water, heat, light, head with holding tank, etc. No shower, however, I was docked in a marina with showers. It's TOTALLY do able. It just takes a bit of getting used to.
In my honest opinion the best way to approach it is to have an end goal in mind. My goal is to have a large blue water cruiser eventually. SO.....I'm living on my little 27 and saving a LOT of money that I'd be spending on rent and utilities. I cook on board and live quite comfortably by myself. Living on board in Chicago during the winter I'm sure would be hard but if I chose to do it I'm confident that I could.
One thing you need to think about is where will you be going for grad school? Will it be a coastal area you can cruise to? Or, will it be on the other coast where it wouldn't make sense to sail all the way around. Maybe the boat you need needs to be trailerable.
Personally I like the fixed keep boats with inboard motors. They (for the most part) take rougher water better and are more stable. Its just a personal preferance. There is no right answer. Find what works for you.
My advice is to see as many boats as you can within your price range. Then, take a look at the final few with someone that knows about fiberglass blistering, structural imperfections, botched up repairs, etc... If nothing else, you want a good solid hull, deck, and mast. Cosmetics and everything else you can work on yourself if you're the handy type.
I was able to find my Cal 27 for $5K. Its not perfect, I have some minor problems that I'm working on in the deck, but its mostly cosmetic. Other than that its in near mint condition with an inboard motor in great condition.
Hope that helps. It's just my 2 cents.