I knew a single guy that got tired of cleaning his house, washing dishes, etc.
He threw out every dish expect one, all of his silverware except one set, all of his chairs except two (a kitchen chair and an easy chair), etc. Don’t know about the socks!
My answer would be 20. Actually maybe just 7 darks, 7 whites. But a few spares of each would be good. Give them to the Goodwill NOW. He’ll never miss them.
If you go throwing out a man’s socks you better be prepared to stay on top of the laundry situation. That’s why we horde these things, we don’t like to do laundry when we’re single, and we have a fear of being dependent on somebody else when we’re not. So we have lots of socks and lots of undies and can generally go at least a month without laundry being done.