I'd say wrong forum at least for the Digi Back part. The Mamiya RB67 Pro S is a superb camera fully mechanical so if you want to take the digi route the RZ might be a better choice it's electric. Also the RB67 with film Back has more resolution than the 22 MP Back. Think about going hybrid if you absolutely must go digital shoot film and scan it or better get an optical enlargement. Instead of buying outdated equipment you might consider renting high end equipment it's cheaper and you always get serviced and well maintained tools.
Thanks for your answers.
I think I won't be bothered at all. I'll keep shooting and scanning
There's nothing promising on this path unless spending $$$$$.
I do not think digital backs work on the RB. I used the ZD 22 on my RZ Pro IID and it was phenomenal. The downside is high ISO and exposures over 45 seconds. I highly recommend it otherwise.