Should I be buying another lower? Should I buy different uppers? Should I buy the remington 700 I've been looking at? Ammo? Suggestions I have about 2500 to spend and want to maximize it.
The lower on an AR is the registered part - so if you're short on cash - buy the lower, and get a stripped one to maximize your current wad of cash. The upper and all the rest of the pieces of an AR - are unregistered parts and you could order them mail order and get them sent to your house - barring any massive changes in the law that is. I've bought four different uppers over the years - and every place just shipped it to my house once I paid them. Shotguns are less likely to get regulated than black killy rifles - so I would prioritize that one lower. The price of ammo is only going to go up in a ban - and will also go up just because of the crappy economy/inflation in general - so I would spend money on ammo.
You might want to think about spending some of it on things that will prove useful during a ban and/or massive price increases: reloading equipment.