I was in the same situation last year. On the one hand, I am married and my wife all for getting a dog too, but on the other hand, I do the majority of the work. If you do get a puppy, i recommend waiting till it is warmer outside; I had to get up in the middle of the night to let him do his business in the winter time. I was concerned about the time left in the crate as well, but I always come home for lunch, so for a day where i'm at school all day, they at least had one break. Our schedule isn't usually all day every day, so there are some days where I get to spend a lot of time with them and there are other days where i just keep them up later at night to burn off some energy. I also don't study at school, if I was out of the house until midnight every night, it wouldn't be fair to the dogs. By the way, we got our first dog right after school started, and our second dog this spring; boxer and blue tick mix.
I agree with the financial concerns, but you're going to have to make sacrifices eventually; it's just a responsibility you are going to have to face, but I personally feel that it has been worth it. We also signed up for dog classes, so we would spend an hour once a week with a group of people that weren't affiliated with med school, which was a nice break. i think my boys help keep me sane!
As for going away, boarding does cost, but more than likely you're going to meet people that aren't leaving when you are, and would love to take in a little dog for a short time. We have personally done it for friends of ours; at one time we had 4 dogs in our house...that was a little much.
I really like having dogs during school. They usually just sleep at my feet when i'm studying; I love them to death, they are great study partners.