I have had the D700 for many years now and I still love this camera. So I think the D600 is the best choice for a camera that will last you as long as you would like. For real estate photography, you certainly want something wide and a zoom is sometimes convenient/quicker. So look at the 16-35 f4 VR and the older 17-35mm 2.8. If you want a single "do it all" lens, go with the 24-70 2.8 which is sharp and has great contrast. If you find yourself getting budget strapped because of the expensive camera, you could go with prime lenses and just use your feet for zoom. Primes are tack sharp. I would choose a 20mm for the wide and 35 or 50mm for mid. If you don't have a speedlight, it's probably a good idea to get one for fill lighting when necessary.