I actually do have those 3 primes but I was suggesting 21 or 24 or 35, they are totally different and in my opinion are about the best glass you can buy. Most people would be happy with any of them. My favourite is the Zeiss 35/1.4, it is the best lens that I have used but comes at a cost. The 24/1.4 is another fantastic lens and is unbelievably easy to use and the results are superb. The Zeiss 21/2.8 is in a class of its own for landscape work and has a cult following. I would suggest a search on Flickr for any lens that you are considering, you will see a heaps of examples.
I have the 5DMK3 and the weather sealing is about as good as you can get at the moment. I only recently bought a "raincoat" for my camera so I don't have any experience with weather extremes. It might be hostile crowds and thick weather that I have been dodging. Anyway, I don't want to get them wet if I can help it and tend to not worry about shooting in torrential rain. Don't get snow where I am.
I thought the whole point of this thread was that you were going FF so the 7D shouldn't enter into considerations.
As for the use of those primes, there is obviously some overlap, I picked up the 24 first, then the 21 as a bargain and paid a lot for the 35, I can't sell any of them. They are just way too good to part with. I use the 24 the least, but I will never ditch it. I use it mainly for environmental portraits.(parties) The 21 is for landscape. And the 35 is a walk-around lens in conjunction with the 70-300mm, this is a killer combo, that I think has no peer as far as IQ goes and is just a dream to use.
As stated in my previous posts the 24-70 or 24-105 are still the handiest lenses to have. I have a 24-70 and I still use it for weddings, when brides want quality shots, this lens does it very well and it does it easy. In my first post I said that if I'm shooting for somebody else, I use a quality zoom, when you have to get the shot. If I was on a holiday in a remote place and I needed to record my adventures I would use a quality zoom, because I know with my limited skills, it would be just one more thing I wouldn't have to worry about.
As far as the nex7 goes, I am saving for one of them now, I think they are very special.
All these different combinations make your head spin, I know, I have been there, but I firmly believe there is no one right answer and every consideration here is offered with good intention, so in the long run you make a choice for yourself and know that at the time it was right and you might eventually, change your mind.
Doesn't mean it was wrong.
Good luck, can't wait to see some of your photos, with whatever combo you choose.