The Mamiya lenses are narrower diameter than most all the canon EOS lenses, and lighter too I think, so on balance, a smaller package than a 5D and lenses.
The meter is the same between the 7 and 7II. The only differences are the 7II offers is a polarization layer on the rangefinder window (debatable value - really not noticable unless shooting into the sun), and it has a multi-exposure capability. The negatives are the 7II's darkslide wind lever is seriously flawed and far inferior to the one on the regular 7. I've had both bodies at the same time, and later sold the 7II as it didn't really offer anything over the 7.
All the lenses are great. The close-up adapter is a bit kludgy but optically excellent. The polaroid back is best if dedicated to a 2nd body. It's not really feasible to switch it on and off a single body to interchange with normal film use.
Bottom line: the Mamiya 7 is easily the best 6x7 rangefinder available, and I think in many ways the best medium format system available. (I have an RZ system as well, and that is better for the few things the Mamiya 7 is not great at: long lenses, close-ups, portraits, fast lenses).