I think you should decide on a format. 6x4.5 and 6x6/7 are much different beasts. From my limited impression here, I think you'd be happy with a 6x4.5.
You could get a rangefinder type system, but they are typically expensive. So that leaves SLR style systems. There you're looking at Mamiya, Pentax or Bronica. Mamiya can be had in AF or manual focus (the AF is a lot more expensive). The Pentax system can also be AF or manual, and there isn't as big of jump in price between the two. Bronica is only manual focus.
I think that Bronica will probably be the cheapest. Mamiya and Pentax about the same. All have a good range of lenses. All are about the same size. The Bronica is probably the most bare bones, the Mamiya the most refined, the Pentax the most modern-feeling.
Don't worry about 220 film. There's only one type of film made in 220 anymore and it's Kodak Portra, and it's stupidly expensive. In most cases, one roll of Portra 220 costs more than two rolls of Portra 120. Stick with 120, it's actually going to be around for awhile.
I like Bronica cameras, but I don't have a ton of experience with the other brands.