NewRy, I am a Michigander too, zone 5 (5b I guess is the new terminology). Don't know a thing about cannibis but with a nephew that suffers from PTSD (Army) I can understand your need. And BTW, thank you for your service! I am in the throws of research for building my own greenhouse and one book that might be of interest to you is Mike Oehler's "The Earth Sheltered Solar Greenhouse Book". That lovely polar vortex we just had was a rude reminder of just how cold it can get. He was located in northern Idaho and had 20 below temps too. I got the book on my kindle for about $10 (couldn't find it at the library). Easy reading and he also tells of his errors as well as his successes. I think you could get a good idea of how to put something together cheaply and easily for a good trial run to find out if you liked it, without getting too involved. At the very least you could extend your season. Have you considered cold frames?
