If you're planning on keeping them in the brooder until about 6 weeks, then 2 sq.ft. each will work. I've managed 1 sq.ft until 3 weeks, but it was just too tight after that. It felt like they were walking over one another, and the bedding was needing cleaned FREQUENTLY. If you have the space, I'd rig something up 4 x 8, primarily because a 6 ft. or 3 ft anything will waste lumber (unless it's a size you have on hand). You could always reuse the boards after you're done with them.
Pine or aspin bedding are good choices in the bottom. You can add it right from the get-go or wait a day or two. Sometimes they sample it. I've never had issues with them finding food/using the feeder (just peck at the feeder with your finger-like a beak - once one eats, they all play follow the leader). The last time I brooded I covered the bedding with one of those nonslip rug mats; the things you put under area rugs to keep them from sliding - just for the first two days. Just shake it out and throw it in the washer when done.
