AV1200 series can do 16 points easily. You totally do not want 16 WLAN APs in the same building though. You will create massive signal overlap.

tp-link publishes this and it is different for different adapters.

http://www.tp-link.com/en/faq-434.html

Keep in mind, the powerline bandwidth is shared between all the adapters. For example, with the wpa4220 the powerline bandwidth is 500mbits/sec. If you install one wired pa4010 by your router, and 10 wireless access points, each access point will get no more than 50mbits to the router on average. I'm not sure how the efficiency holds up with so many access points, I've only got three and I'm adding a fourth. But for web access it should be ok. The gigabit models are faster of course. For 2.4ghz networks I've had good success alternating between channels 1 and 11 in a checkerboard pattern. You can get 40mhz channels that way (300mbit 802.11n 2.4GHz), and the signals don't really interfere.