Welcome! I think it's a great idea to live separately for now. You're already going through some huge adjustments in your lives, and that will give you both some freedom to settle into your own new unique circumstances.
How much time he has will depend on his study habits. MS1 and part of MS2 were pretty similar to a heavy semester of undergrad for my husband. He was usually done with class by midafternoon, so he would mainly study while I was at work. Before tests, he'd study a little more in the evenings, but having dinner together was never a problem. He even did a lot of the cooking, housework, and grocery shopping, since my job required relatively long hours. During MS2, he started studying for Step 1 of the board exams, and then it got pretty stressful. He still made time for dinner with me, but he needed to do a lot of studying, so I was able to help him out by taking over more of the household chores.
MS3 was his most difficult year of medical school. That is the year they start doing rotations in the hospital. Depending on the program, students may have to travel for some of these, but my husband didn't. He'll put in a lot of hours, and he'll start taking call, so he will be pretty exhausted most of the time. He'll also have to study a lot more at home because he's basically learning a completely different profession every month or two. Since this will be his first real hospital experience, he will probably be a mix of excited/happy and sleep deprived/hating life.
MS4 for us was a great year. If you are planning on getting married during medical school, this would be a good year for it. With his program, they had the option of not having rotations every month, so he used a couple of months for residency interviews. You could easily fit a honeymoon in there. The rotations were a lot lighter, too, and he didn't have call as often, so you'd have plenty of time to get settled into your marriage before the joys of residency start.
As far as advice goes, he'll need you to be supportive and keep him grounded. There will be times when the stress really gets to him (not the time to remind him that he's pursuing his dream), and there will be times when he gets too wrapped up in the pressure of it all, and you have to force him away from the books for 30 minutes to go get an ice cream cone (or, I guess in South Dakota you'd go for hot chocolate!) You also have to make sure you take care of yourself. You're moving to a whole new city, and you will need to make friends of your own so you'll have someone to hang out with when he's working or studying.
Finally, a little bit of a warning... This probably won't apply to your relationship, but I just feel like I should say it. Some medical students change for the worse. If he starts treating you disrespectfully, you need to address it right away. You are there to support him and determine if he is the man you want for your husband. If he can't support you and love you as well as medicine, then he's not ready for the complications that come with having a medical career and a marriage.
