Just a small point about Mamiya TLRs - if you're handholding, they are infinitely easier to work with if you have an L handle attached. I seem to have one still in my equipment cupboard (TLRs long gone - liked all the lenses except the 55 mm, which took a lot of stopping down to get sharp edges).
Another point - somebody was talking about DOF preview. As I recall, there was a 105 mm lens for Mamiya with an iris diaphragm on the viewing lens to get over just this problem.