There is a list of good .223 brass to use, best is around .012 wall thickness. Some is up to .017 thick and creates problems. I cut at the shoulder, size, and trim.
Take your time and research the barrel and Bolt. Don't get caught up in blowing money on bolt and mag releases crazy rails you will never use. Research each part one at a time. Buy once. Take your time. Make sure each part fits your needs. I.e don't get tactical if you want a hunting rifle.