hah, enjoy your internet I love TP-Link gigabit wireless routers, I think they all work wll, at least for me it is

check your subnet mask, how can you access the router in another subnet? two solutions, set you first router's ip address to 192.168.1.12, or set the mask to 255.255.0.0

if you do not connect the wan port, how shall the internet access LED turn on? access point is only work on layer 2 to forward packets, take little care of the LED status if it work fine.

are you finding the firmware 1.2.1 Build 20180328 rel.2212(4555) see this link and find it: https://www.tp-link.com/uk/download/Archer-C9.html#Firmware

yes, though c50 is ac1200, but the wan port is only fast ethernet support 100M maybe you can find a new router with gigabit ethernet support 1000M, such as archer c1200 and one more thing, before you...

i think you can pick out the power cable, then pick in again, if still the problem, wait about 2 minute, then press the reset buttion for about 10 seconds