There's really not a whole lot of sense in moving from a D5200-a D7100 in terms of image quality. They're roughly the same. Your next "big" improvment would moving up to a FX body or lenses, which would be the most obvious path. If you want lenses, I can recommend a few. The Tokina 11-16 f/2.8, Sigma 17-50 f/2.8, Nikon 16-85 f/3.5-5.6. If I were in your current situation and wanting to go FX, I'd keep your money for now and continue to save up. Sometimes the best investment is upgrading photographer him or herself. Not the gear.