Great choice Ailsa, when I was looking for a MF system it was either the Mamiya 7 or the Hassleblad. The blad won out, but not because it was better, only because it had more lenses available. Happy hunting.
I've had one for years (with just the normal lens) and I love it! Only my Rolleiflex with f3.5 Planar lens can match the sharpness of the Mamiya's optic. It is just about a perfect camera. If I could change anything I would make it more robust (the film winding mechanism can be broken if you abuse it, just like the old Bronica S SLRs, so wind on slowly) and I would give it at least 1 mechanical shutter speed that was battery independent. Enjoy and please post results!