Good news for you, if this size is the largest you will need, as the savings compared to new must be quite considerable.
The only question that would linger, with me, is why the guy decided it was too small after such a short time and whether one should have looked for a larger secondhand mill in the new year! But a deal is a deal and at least you might expect to be able to trade up in size, if necessary, for less total cost.
It will get you going and give you some experience earlier than expected. Maybe the seller can enlighten you on some of the tooling he has retained which was less needed, at the starting point, with the mill?
My advice, for what it is worth, is to buy better and fewer cutters (so avoid cheap sets of special offers), except, perhaps, for an initial set of cheap cutters if you think you may destroy them accidentally due to inexperience. In hindsight, sharpening kit was more important than actual cutters, back when I started with my lathe….
Until recently, I had sufficient end mills (of dubious quality) but never (it seemed) the size or type I needed for the current job.