If you bought them from a feed store, they are probably BBB, so I would not name them and plan to be processing them in about 6 months or so if they are. Sorry, but BBB are not a long lived breed. I hope they are the, Standard Bronze Heritage breed, for you sake, so you can keep them for pets...
A 20'x40' is a lot of coup for just 20 chickens, but I would suggest you get another roo, because if anything happened you won't be able to hatch any chicks from infertile eggs and 1 to 19 is a hit or miss ratio. Most people keep 1 roo for no more than 10 hens, but that's just a suggestion, of...
At 2 weeks old, you should not need a chick, but you will still need a heat lamp, a cover over the brooder and under the lamps, so they will not break the lights when they start to fly, and a accurate thermometer. I have my brooder at 90 degrees to start with and drop the temperature about 5...