I wanted to address a few things, First off, I own the Mamiya RZ67 Pro II, it's a great camera, I also own the Polaroid back, there is only one polaroid back, the 545 is for large format backs so that won't at all be part of what you're looking for so don't worry about getting the wrong back, all the RZ polaroid backs take the same film.
Second, the OP said he wanted to use the RZ67 ONLY for the polaroid shots, and would use his Digital for the rest of the wedding, so weight isn't an issue (also the digital he uses is as heavy as the RZ67 just handles easier.
Third, polaoid pack film (fuji fp100-c and fp-3000bw are NOT discontinued... what is discontinued in the US market is the 4x5 versions called fp100-C-45 and fp100-bw-45 respectively... B&H is almost sold out of the last shipment of the 45 version and they are obvious because they are $40 a pack instead of $8 a pack, so the OP won't buy the wrong film... ) The normal fuji versions for the mamiya or similar camera are still in production, both B&W and Color versions. Yes the RZ67 can be stopped down to handle 3000 speed film, also for inside shots near a window or something, 3000 is perfect for a bride, really artistic images can be created with it.
Fourth, I also use my pocket wizards to fire off the RZ67 Pro II camera with studio strobes, it works great, BUT you MUST buy the NEW pocket wizard Plus III because the Plus II version isn't oriented correctly and gets in the way of the focusing knob on the body of the RZ. There's one work around, if you own the canon or nikon specific pocket wizards and got that little "interference" in between adapter thing, it's a small piece of metal and plastic that extends the height of the hot shoe slightly (and prevents interference if you add an on camera flash on top of your pocket wizard) anyway this little piece will extend the Plus II high enough that you can attach it properly, that's what I used until I switched to the Plus III system and realized I didn't need the stupid connector anymore (thank goodness I was always misplacing it).
What else is there... umm the RZ67 is a great camera... if you REALLY think you'll go into digital MF someday, and you have the money... look at the Mamiya RZ67 Pro II-D which is a step up and has digital connections so that the digital back can record information in the metadata about the shot like the f/stop and lens aperture at the time the shot is fired which can be useful. It's not necessary, you can use a digital back on the regular Pro II, but if you've got the kind of money for a 1D you probably can afford the increased cost of a used Pro II-D over the standard Pro II.
That said the Pro II's can be had for a song... I've just moved to LF from MF and I still use my Mamiya RZ but not like I used to, I'm still new to LF so I'm not sure I want to get rid of my whole RZ kit just yet, but I can see myself not using it anymore... if I'm going to have the 4x5 camera case, I don't need to cary around both huge setups and can always throw a 120 back on the 4x5 camera... so I MIGHT be convinced to sell it... and I have a 180mm, a 90mm, and a 50mm lens, Body, and TWO polaroid backs so you can load the B&W and Color, at least thats what I do PM me if you want to make an offer.