I have a UAP-AC-PRO (powered via POE injector) that's doing fairly well in a roughly 1800 sq. ft. split-level house. For those of you unfamiliar with the term, a split-level house has two stories on on one side, and one story on the other side, with its floor halfway between the floors on the two-story side.

The AP is situated on the single story side, but coverage is a bit poor on the fringes of the two-story side, so I'm looking to buy more gear. The UAP-AC-PRO was top of the line at the time, but would you all recommend now? Given new hardware available and new WiFi standards, what would you buy? Is it useful to keep the old AP, or does new hardware obviate that?

I've got four kids and plenty of phones, tablets, and computers. If it matters, internet connection is a cable modem via an EdgeRouter Lite.