***Parts are still hard to find and crazy over priced*** The lower receiver is the weapon. It has a serial number. The rest of the rifle is just parts. Lower contains fire control, magazine release, bolt catch, and the butter tube. Upper contains the BCG, gas system, forward assist, and barrel. They are pretty easy to put together, just take your time. A roll pin punch will help not round out the pins. As far as brand differences, there are endless makers out there. You pay more for better quality parts to an extend but the name is a lot of the upcharge. Just naming a few off the top of my head; LWRC, Troy, Daniel Defense, Rock River, Spikes Tactical, are all good brands. In reality, a semi-retarded monkey can be taught to manufacture and assemble these. As long as the material is good and the holes are in the right place it will work. **Lower** I'd recommend a metal lower receiver, but that is just because plastic weapons bug me. They can be found for ~$400 on Gunbroker right now. I have a line on a few someone got that I could prolly snag for $300-$350 so let me know if you want one. (Send me a PM if so) The Lower Parts Kits are the mess of stuff needed to assemble the lower. More retarded monkey parts. As long as it falls in spec, you should be good. **Upper** The upper is again retarded monkey work. Just make sure it is straight and drilled properly. The barrel and BCG are work a few extra bucks on. They are really the heart of the rifle, and the extra cost for a chrome-lined barrel and a quality BCG is worth it IMO. I prefer a receiver height railed gas block over a fixed front sight due to the options it gives you. A good set of back up irons and you're good to go. I use a metal BUIS (Troy Battlesights)on a railed gas block because I'm paranoid. You don't need a match trigger, four lights, a shiny hand-guard, or extended-snag-on-your-gear junk anyways. Leave the gear queer stuff for the cool guys at the range with their safe queens. Now, all of these parts and accessories are sold out. You won't find parts for decent prices for months. But you won't find ammo to test your new toy for months either. All this is a really quick overview. There are great pictorials for each step online. If you have any other questions as me here or send me a PM.