Someone on Photrio sells replacement latches for the N80/F80 and F100 for not a lot of money.
+1
I don't have a problem with my F100 and I got a latch replacement anyway. Just for murphy's law. You can be careful with the latch -- just open it as you're closing the door rather than slamming the door closed -- and likely be fine for a long time.
Pros, in the old days when they were on film, probably saw this as a major disadvantage because you just want to drop the film in and get to work before the bride throws the bouquet or the pitcher throws the fastball, but for today's landscape photographer, that's all way less of an issue.
I don't have a problem with the battery choice on the F6, personally. I get 20 rolls from a set, I keep spares in the bag, and you can get good rechargables in the size from online retailers as well. But it is super easy to get AAs for the cameras that use them, absolutely.
For OP and medium format, if you're really seriously going to sell large prints doing landscape, that Mamiya 6 is hands down the one that will make the best negative. I don't know the fuji, though I am certain that would be a winner, too. I like Fuji lenses.
You have to really think before going there, though. The Mamiya 6 only has 50mm as the shortest focal length. 55mm for the Fuji. In 6x4.5, a 55mm shoots a field of view about like a 35mm in 135. In 6x6 with a 50 it's like using... I dunno. A 28mm? 30mm? Not a direct conversion because 135 is a wide format, but it's still just the "wide" range, and no wider than the 645, so not "very wide" or "super wide."
Don't get me wrong, I love the bejeebus out of the normal Fuji lenses I shoot in 6x8, but I personally grab the 50mm most often for landscape (FOV is like a 22mm lens in 135). And on 135 I like 20mm and 24mm views better than 28mm and 35mm. When you want expanse, wider than a normal FOV is what you need. Your style may vary.
So... yeah. IF you like a 28mm lens on you 135 cameras, I'm going to say get the Mamiya 6 from that list and learn to love the 50mm lens. The Fuji will be good, too, both way more resolution than tiny little baby negatives in 135.