One other important thing: if you get eggs, or straight run chicks, or any chicks that aren't sex links (any form of sexing other than DNA or them being a sex link hybrid isn't 100% reliable), you have to know what you're going to do with extra roosters. Most people don't want them for anything other than eating. If you don't want to either cull them or give them to people who'll cull them, you need to make sure you'll never have roosters. To do that, you'd want to get sex link chicks, or ones that are old enough to be sexed with 100% reliability, i.e. a few weeks old.
Also, don't assume the person trying to sell you the chickens is fully informed. Do your own research.
First, you'll need a coop and run. 4 square feet of coop per chicken, and as much run as you can give them. And do NOT trust the store-bought coop's assessment of how many it can fit. You're better off buying a shed and converting it, or building it. Check Craigslist for supplies and/or sheds to buy cheap.