He eating yet? I would start some insect colonies now to avoid paying a fortune, then mix in some vertebrates like fowls, frogs and such etc.
Don't really feed beef or to much chicken.
Once he settles in I would handle him so he's more manageable when older (most niles don't ever fully tame tho).
Also be sure to build him a BIG exhibit as they grow quickly, be sure it is secure as niles pose a potential danger to cats and other pets