I have a 5D Mark II, and a 5D Mark III.... but 90% of my portrait work is actually with film. For a year now.
I'd seriously suggest going right for Medium Format, truly. 35mm film is nice, very nice, but really not the same kind of experience or "quality" that Medium or Large Format can bring you.
If you're going to Canon film cameras, I'd suggest the EOS 3 as well. It has a 45 AF point system that is still better than many Canon cameras today! And it's cheap. Very cheap. And you can use all your EF lenses. I have a 1V, which is like Canon's flagship film camera, but it's bulky and heavy.
But really, for 99% of my serious film shooting, it's either 645, 6x6 or 6x7 format cameras I use. The difference in the negatives is SUBSTANTIAL. And makes a huge difference. The old camera systems, many of them, have lenses that are just as good as today, or better in some cases. In either case, it's about lenses having "character". My 80mm f/1.9 lens on my 645 camera (about the same as a 50mm f/1.1 lens on a full frame camera such as a 5D Mark III) has old coatings, and flares a bit weird, but it has more character and such a cool look to the photos in various kinds of light. It's more interesting. And I love it. My other systems, hell, lenses in many cases can be bought for very cheap. There are exceptions there too though, of course. So much variety!
I scanned my own film for over a year. Sucks. Takes a long time to get right, sharpness/resolution isn't great, and it's a big time sink for most people. I put it aside.
The thing is.... the negative is similar to a RAW file, if you want to think about it that way (I'm sure you know this, just saying though...) and depending on what lab (because they use different scanners, with different software, with different people running them) you'll get very different results back. Which can be frustrating.
Let's just say this:
I scanned my own film = 1/10 for happiness of tones and range/colors, etc. 3/10 happy with resolution.
I send it to a local lab that I prefer = 7/10 happy with tones and range/colors, etc. 5/10 happy with resolution.
I send it to a pro lab in the USA (I'm in Canada) = 11/10 happy with tones and such, 10/10 happy with resolution.
The thing is, there are three major labs in the USA that (well there are many more than three, many more) but there are three in the USA that are extremely popular, and people from around the world actually send them film. Myself included. These are (Richard Photo Lab, Pro Photo Irvine and Indie Film Lab, I personally use Indie Film Lab).
These labs will bring out every last ounce of quality and tones/depth from your film photos. The difference is literally MASSIVE.
I'm tired of shooting my film and knowing that there is so much beauty locked inside the film, and knowing that it's a pain in the ass to get it out of there myself. So.... off to the pro labs it goes. Results = better than any editing I can do on my digital. End of story.
Medium Format to me is a nice middle ground.