I don't have any of those camera but do have an Olympus G. The idea of having both the aperture and shutter speed (when in manual) dials on the front of the camera was a rather brilliant idea. But I have always used cameras (even auto exposure) with the shutter speeds on the upper right deck. I just can't get used to the shutter speeds anywhere else. I don't know that it would cause you any problems, but if you think it would, you might want to take one of the others. Other than that I would think that the better camera due to its size and lenses. Just be sure to have extra batteries or a light meter (even an app on your phone).
The idea of an MF folder has merit. I like them. They do give much larger negatives, but only give 10 or 12 shots per roll as opposed to 24 or 36, and normally the rolls cost more. You can probably find 35mm film in Vietnam, and probably even b/w. I suspect 120 would be a little harder to come up with outside maybe some of the larger cities.
If it isn't going to become a weight or luggage problem, a wide angle lens would be beneficial in tight places like some rural villages, jungles/forests, and landscapes. But that might be my style of shooting more than yours.
I hope you enjoy it there and get lots of good photos you can share with us when you return.