when I went from Pentax to Nikon..I made the move as I wanted a 70-200Vr II..plus I wanted a camera that had better AF than the pentax K5 had....I looked at Nikon lens lineup and that too made the decision to go with Nikon easier.
the point I'm trying to make is DSLRs are only part of a system, the lenses are the other part.....most people go with Third party due to cost, when I was with Pentax it was due to a manufacturer lens not being available for the FL that I wanted.
I read reviews, I look at the lenses first hand , up till now the Nikon lens has always been the best choice for me ...but they are expensive, but you get what you pay for I believe...
so if you can stretch for it get the Nikon lens..after all what did you buy a D600 for ..if it wasn't to use Nikon Glass ?
as far as your lens choice...I love my 70-200...then the 24-70...so Id get a 70-200 first...its the most expensive , so get that pain out the door early I say ...but if it were between a 24-120 or the 24-70, Id buy the latter
I would prefer to buy only one lens and it be outstanding, rather than three ok ones for the same money YMMV