Wait!
STOP RIGHT THERE!
DON'T buy a 2014 Mini... from anybody.
If you're going to buy a used Mini, get a 2018 Mini.
MUCH better Mac.
It WILL cost you more.
But it will be $$$ well-spent.
You can still get Apple-refurbished 2018 Minis, which will look almost "new", and will have a 1-year warranty, as well (you can even get AppleCare for them).
Get 16gb of RAM and at least a 512gb SSD.