I have the Pro so I have interchangeable backs. I've never handled one of the earlier ones.
I don't have, nor have I used, one of the left hand grips. I have the winder grip, which is a right hand grip. The camera handles great with it, even if it is a bit big and heavy.
The right hand motor grip for the older versions (not the Pro or Super) is very large and noisy, and it can be hard to find one that includes the necessary coupler.
Rumour has it though that the thumb operated winder designed for the 645e may work with some of the older models.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
I have an M series from the early production. I can't say how many rolls I've shot but it's in the hundreds. I have nearly all the accessories and extra inserts, I even have the original case. It's a fine camera. I'm partial to it despite having to tilt it for vertical shots. It's never failed in me. I've replaced the seals once and that's it. Have fun with yours. I did but a Pro model a couple years ago. I have a nicely equipped RB67 Pro S too and the revolving back is a delight.
My preference these days is large format though.
Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand
My 1000s has the AE prism, which is great for quick shots. This is an aperature priority system with the shutter speeds being selected. If you really like the camera this might be worth a look. For indoor shots a Sunpak 555 is used with 6 x 6 mount, letting the flash to be used in automatic mode. I like the fact of getting 15 exposures out of a roll of film, Steven.