Having extra junk all over is actually helpful during integration, as are the extra feeders and waterers. So don't feel like you need to clean it up, but do make sure there's no spots where a younger bird can get trapped and cornered and left with no way out.
Since they're so young you might be able to get away with just putting them together (though I'd supervise for the first meeting) or fast track with a shorter see but no touch period (like a few days up to a week). It shouldn't take nearly as long to put pre-teen chicks together vs older chicks...