Just stick with your 16" barrel and spend the money on ammo.
After you shoot it for a while, *then* decide what accessories or other uppers/barrels you want.
Owning an AR-15 is an expensive hobby, don't go running out and buying a bunch of stuff that will soon enough be sitting in your parts bin. Wait 'till you know what you need.
We've all been there, and we've all spent money that could have been better spent -- just trying to save you a little $$$ (and heartache).
Go shoot, be safe, and have fun!