Hey folks! Name's Gus - washed up digital photographer gone film! ;D

I've been shooting 35mm for fun for a few years now and have finally given into the MF bug. For a while I was interested in the Mamiya 645 for it's modularity. I figured 120 was the next step up. However, my goal is to get even REMOTELY close to shooting wonderful b/w portraits like this,

(I apologize but I do not know the photographer to credit.)

I want MF because I want as much possible information in the negs. (I already develop/print at home) That brought me to consider going 6x7. So my question is, what do you guys/gals think about the Pentax 6x7? It doesn't offer modular options - is there something that does? Does it really matter that I cannot switch film cartridges mid-shoot? I've been keeping my eye on this Ebay option - http://www.ebay.com/itm/321085249452...84.m1423.l2649 Seems like a good deal but I don't know the market for these very well. Thoughts?

Thanks so much everybody.