Generally i normally have 2 drives in PC,
one for windows and anything that will need to be reinstalled with windows.
one for everything you don't need to reinstall with windows + games
but i have more space than normal now and don't use much.
So I answered based on that idea. If you want games on there, I would get over 500gb at least.
It doesn't help to fill an ssd to full as they slow down if they don't have about 10% space free
As Bob says, its easy to fill drives up (everyone is different, I have 4tb of space but have plenty of free space still)