I think it's all about choosing the right dog. Get a puppy now, and you'll likely be overwhelmed even w 6mo of housebreaking/training under your belt. If you get a dog that is 2-3 yrs old, medium energy, and happy-go-lucky, then you'll be all set.
I am doing a prelim yr in medicine and have an American Bulldog (80 lbs of smoosh and love). He's 7yr and I've had him since he was a puppy, so he's used to the routine of long days. I exercise him a LOT when I am around, so he generally sleeps when I'm not. Also, I have a dog walker that comes EVERY DAY that I work (floors or ICU, not electives), even on the shorter days (10 hrs). It's just a pee break not a long walk so it's cheaper ($11/walk). But they send a pic/text every day.
Having an unconditional wiggle-butt greeting every single day not matter what is invaluable in such a high stress job. Yes, it could end up a disservice to the dog if you do it the wrong way (choosing a high energy or nervous dog or a puppy), but the situation has potential, esp since you are clearly willing to try dog walker/daycare. Even one day of daycare during the week + walker on the others could be great. It will also help to practice gradually leaving the dog for longer periods of time before inter year actually begins, so that it will not be a total shock. IMHO, definitely a shelter dog is the way to go, but please make sure you choose a shelter that does temperament testing, so that you know what you are getting. (Ie, good w kids if you plan to have kids in the future, energy requirements, etc).
Good luck and feel free to PM me w questions, although I'm on the site intermittently.