You could shoot the vast majority of any wedding with a 5d2 + 24-105, and never be undergunned. If you need an available light situation, sure, a 50/1.4 is fine.... but then again, you'll need to be careful, as DOF at such wide apertures does not bode well in a lot of situations when shooting at a wedding. Folks want reasonably sharp images.... I say reasonably because they don't pixel peep. We do that for them.
Given your situation - and assuming you're going to take a little time to get to know the DOF characteristics of shooting FF, I'd get that 5d2 if you feel the price is right. Shoot it with the 24-105... and unless you're shooting in a very very dark place, you'll do fine (or... if you have AF assist on flash... you'll also do fine).
Take the 50/1.4 and stick it on the 5d3 and you're set to go.
Keep the 7d as a total spare.
Back in 02, I shot 40 rolls of 36exp c/n film, or just over 1500 exposures at Dragon-Con in Atlanta. All in one afternoon. Cameras were an M4-P and an M6TTL - two lenses a 35/2 and 50/2, and thats it. Weddings, when I did them, were a pair of 500 Hasselblad, with 60 and 80. Thats it. Half jokingly I say... quit bein' spoiled by technology and concentrate on image and technique more than hardware.