Are you channeling your best self with this comment? (If you're not sure, check out our Code of Conduct.)
Stephanie is the Head Recipe Tester of Food52.
Usually a half pound of uncooked potato per person is a good place to start. As long as you have space for leftovers, there is no harm in going over.
Cynthia is a trusted source on Bread/Baking.
For holidays, I usually count 1 1/2 potatoes per person. Everyone gets as much as they want, and you have those heavenly leftovers. At a more sane time, I go with 1 per person.