looking at building a new 9mm caliber ar. whats the best sight to order uppers and lowers. Never built an ar but have read alot about it. most places point to palmetto state armory as the place to get uppers and lowers, any other reccemendations? is all i need an upper and complete lower besides sights? Do i need to get a 16 inch barrel or can i get a shorter one and it be considered a pistol? like i said, never done it before and was wanting a 9mm cal fun little carbine to shoot. Thanks for all the tips.