Welcome back. I don't post here often as I do mainly wildlife. But when I started, and what i did in school was landscape. I too have gotten the bug to do more. The D750 is a great camera. I have a D600. Went to that from a D300. I miss the crop factor for wildlife. But for portraits and landscapes it is awesome. Even wildlife is great if I can get close enough, so not to need to crop a lot. Then they look amazing. Go full frame. You won't regret it.
Bill