It depends on what you want to achieve. If DOF and perspective do not matter and you r just lazy to walk, cropping it to DX saves the time cropping during post-processing. Else, just walking nearer to the subject would ensure that DOF and perspective remain unchanged.
As for the second question, like I told u try not to ditch the 24-85 coz it's really a good lens with very useful focal lengths of 24mm, 35mm, 50mm, 85mm. If u really need to ditch, the 18-35 would be a lightweight replacement, albeit trading VR for wider angle. For me personally, I would have retained the services of the 24-85 for generic shooting and use the 50 prime for low light. Then for wide-angle landscapes, I would save up to buy the Sigma 12-24mm since 24mm is tight for wide-angle landscapes. Ultimately, the decision to buy what lenses still depends on your priority: buying to fulfill the focal range gap or buying to fulfill the types of usage?
Thanks. Maybe it is good to have multiple lenses for different purposes. I used to have 3 primes , 40 f2 and 2 x 50 f2 just for different purposes and effect. Perhaps the 24-85 can co-exist with either the 16-35 or the 24-70.