A LOT of good advice here. Let me step in with a consideration I haven't seen yet. Some of these cameras, especially the Mamiya 7 and the Hasselblad, hold their value remarkably well. Meaning, if you buy a Hasselblad and a couple of lenses, it will set you back, but if you don't like it in a year or two YOU CAN SELL IT FOR WHAT YOU PAID FOR IT! That assumes you've taken care of it and the film industry doesn't just disappear overnight (knocking on wood).
I had this experience with a Leica M4 and a few lenses that I recently sold for a bit MORE than what I paid for it when I decided to get a Mamiya 7.
This may also be true of the RZ and RB and others mentioned, but I am not sure. The upshot of course is, go ahead and get the best you can afford and make sure it's one of these that really has been stable in value and you really cannot go wrong. You can try it and then switch if it doesn't work.
When I first started shooting MF, that's what made me go for a Hasselblad. I wish it was 6x7 format bcs I love that aspect ratio, but it is pretty easy to carry around with a few lenses and backs and super flexible. The Mamiya 7 is less flexible but a marvel of sharpness, lightness and ease of use. And if I change my mind and sell them, I'll probably be out very little money.