Based on several reviews, the Sigma Art 24-105mm f/4 is slightly better than the Nikon 24-120mm f/4 and it's also cheaper (the Nikon will be cheaper if you buy as a kit lens bundled with D750). It'd be a good walk-around & travel lens before you invest more on great prime lenses.
The Nikon 50mm f/1.8G is also too inexpensive to ignore.
For tele zoom I'd go for Nikon 70-200mm f/4, arguably the best value and paired well with the D750.
For wide-angle lens I'm thinking Sigma Art 24mm f/1.4 for best quality or Nikon 18-35mm f/3.5-4.5 for best value.
The Nikon 50mm f/1.8G is also too inexpensive to ignore.
For tele zoom I'd go for Nikon 70-200mm f/4, arguably the best value and paired well with the D750.
For wide-angle lens I'm thinking Sigma Art 24mm f/1.4 for best quality or Nikon 18-35mm f/3.5-4.5 for best value.