Sounds weird (I know).
Why do you want to go MF ?
If you don't know anything about it you also don't know the advantages.
Although I shoot digital with a Leaf A22 on the Mamiya 645AFD/II I also shoot some film and I love both.
HOWEVER I would not use film for my day to day commercial work for the simple reason that I PERSONALLY find the digital to be much better than my film.
The look of B&W is stunning but for color I love digital.
When you are switching to analogue only I think you are doing away with a lot of advantages of digital and paying a price that is probarbly too high for each photo.
I would in that case rather invest in a good 5D.
What alot of people forget is that although film and processing is not that expensive, getting the negatives in your PC is.
The best/cheapest solution is the Epson V700 flatbed which retails for arround $600.00 for anything less I would not even bother.
But if you want the absolute best you need a dedicated film scanner going up to $2000.00 (maybe second hand for half).
That said.
I absolutly love the DOF and 3D look you can get with MF.
I would however choose digital with film and not film only.
That said 2.
If you want a good system with options go for the Mamiya 645AFD/II.
It's an open system and you can add the cheap ZD back later on or the leaf series.
Also Phase one is starting a coop with Mamiya meaning there will be some interesting things developing next year (quicker than you think).
Also the Mamiya lenses can be had very cheap on Ebay.
I would not advise to hasselblad although I love the name
Lenses are more expensive and equally performing.
The new system is a closed system and the older (pre-H) are not AF.
Have fun and let us know what you decided.
Greetings,
Frank