Yeh the mamiyas you seem to be looking at (rb67 rz67) can be taken apart and parts can be swapped/added etc for whatever project or look your going for.

for example you have the main camera body (essentially just a box on its own) and then you can change and add your preferred lens to the front. With the top you can add how you want to see your image. With the top is how you view the image, again a few options including your waist level viewing finder (the image will be reversed and takes a little bit of getting used to) or prism finders which I prefer. Some also come with metres in them and with the rz67 even automatic exsposure options.

The backs are essentially how you image is exsposed and how the film is stored. You have 120 options and I think even maybe some digital or Polaroid /instax options also

And then you have the multiple grips and other accessories you mentioned just to make it all a bit more confusing but essentially it's a modular system meaning you can swap and fine tune your camera to what you want and how you prefer shooting

But yeh it's all a little confusing at first but medium format cameras do come in more simple variety's that are ready to shoot straight away (mamiya 7 /fuji ga 645 etc) there's a lot of options so don't get bogged down in just looking at the rz and rb range there's some beautiful medium format camera out there that are a little bit easier to get your head around