Id try feeding it this week sometime, its always nice to know whether its feeding or not, early on.
In most cases for aggressive feeding ball pythons, the stress related to nixing everyday, etc...shouldn't be a problem if it was eating prior to you buying it.
The nix will last for months, if not years,
However, im not sure how good it is over a years period.
I have a bottle of nix on hand, which i have only had to use half of it so far. and have gone through two 1 liter water bottles.
i use 1/4 of a nix bottle or so per 1 liter spray bottle of water. every 6 months i change it, just to be on the safe size. So one bottle of nix lasts 2 yrs IMO.
Goodluck, let me know how it goes.