Yeah that’s a good choice, the only reason that I didn’t go for the 6D is that the plastic body put me off (as stupid as that sounds), I wanted the Magnesium alloy body, after the D7000 being Mag-Alloy I didn’t want it to feel any less solid, it sounds stupid but things like that really grate on me, I’m really partcular about the quality of things. But yeah you’ll love it!
If it’s one or the other then I’d definitely go for the primes, I’d love the 24-105 for a walkabout lens but I’d much sooner make the most of the FF DoF with an F1.4, F1.8 etc prime.
Yeah that’s the same as my plan, I’m currently looking for a Non IS 70-200 F2.8L and then after that I’ll be looking for a 17-40L.
Coming from a 600D you’ll appreciate the nicer user experience with the 6D such as the bigger viewfinder (the one on XXXD cameras is like looking through a keyhole) which will enable you to frame your shots more easily, plus it’s just nice to be able to see what you’re shooting. Then, there’s the bigger body that is nicer to hold and feels more substantial in your hand, and once you get an L lens on it it’s even better again, I’ve used quite a few since getting my 5D2 and my 50 just feels like a toy afterwards despite being quite well made for a 50.