I like your suggestions. A little research shows the Mamiya and competitor Bronica look like good contenders. I like using fill flash so I might glance at the etrs (?) for a bit. I spent all my time researching 6x6 and larger cameras because that is what I found in flea markets. Some KEH models of the Bronicas are in my price range so far!
You will probably be very happy with either Bronica or Mamiya. I think the build quality of the Mamiya is a touch better than the Bronica, especially the backs. I've made plenty of great photos with both brands.