TL;DR Version: When using a TP-Link OC200, where should DNS settings be made?

Info:

I have the following equipment: TP-Link TLR-605; TP-Link OC200; (3) TP-Link EAP-245 's; (1) TP-Link EAP-225; (1) TP-Link TL-SG2008P; (1) TP-Link TL-SG2218 and (1) TP-Link TL-SG2218. It all works great! Love it!

Recently, I did some research and found the fastest reliable DNS servers and decided to use them with my setup. Using the OC200, I then set my Primary and Secondary DNS Servers here:

• Settings, Wired Networks, Internet, WAN Mode, Advanced Settings

• Settings, Wired Networks, LAN, DNS Server, Manual, Each of (3) LANs (LAN, Guest, IoT)

• Devices; (Each of 4 EAPs); config; IP Settings; Static Mode (I want the EAPSto have fixed IPs)

That's a total of (8) places I've made primary and secondary DNS settings. It occurs to me that, assuming I want all of my clients and devices to point to the same DNS servers, maybe I only need to set DNS servers at the WAN setting (1st bullet above) - and the rest of the settings are not needed (?) because they will look to the setting made for the WAN.

So, I started to test this out.

• I deleted the DNS settings from the (3) LANs (bullet #2), they then pointed to the gateway/router (TP-Link TLR-605). This may be OK if the TP-Link TLR-605 then uses its DNS settings - but I'm not sure that's what occurs.

• I then started to delete the DNS settings from the first of four EAPs with static IPs (bullet #3 above). The following warning appeared, " Without Preferred DNS server, some functions may not be available including mail logs, setting the controller URL and getting time from the NTP server." So, I stopped.

Questions:

1. With all the above in mind, should the DNS setting for the WAN (top bullet) be sufficient?

2. If I remove the DNS settings from each of my (3) LANs, will they then just use the gateway as their DNS server - which points to my desired servers?

3. Is the warning message because I set the EAPs up with static IP addresses and the individual DNS server settings are needed?

Thanks a lot for listening and any guidance you offer.