x2Keep them four weeks or so. There is a small chance one might be a rooster, or you might lose one. In the meantime you can look for a neighbor or friend who wants them. Once they're past a certain age and you know which ones you like and which ones you don't you can sell the rest on craigslist or maybe a local community classifieds site.
This year I bought a set of 25 chicks from a hatchery and I'm going to try to sell the extras locally so we'll see how that goes. If it doesn't work out we'll have 20 expensive little dinners.