Upgrade 3-Router WLAN with new ASUS routers

[rsbrux]

My current WLAN consists of 3 routers, including an ASUS RT-AC68U serving as gateway and DHCP server. It is daisy-chained to two older models from other vendors:

cable modem
|
RT-AC68U (stock firmware)
|
old D-Link router (stock firmware)
|
older TP-Link router (Gargoyle)

I would like to upgrade the configuration to something like this:

cable modem
|
new ASUS router (WPA3 personal and traffic monitoring)
|
new ASUS router (ditto)
|
RT-AC68U (ASUSwrt-Merlin)

in order to support (AI)mesh routing.
I need 5 LAN ports on the last router, which is why I installed Gargoyle on the TP-Link and plan to install Merlin on the RT-AC68U.
I am assuming that the newer models have better performance than the old RT-AC68U, which is why I plan to move the RT-AC68U to the end of the chain.

1. Is that true that the WAN port used as a LAN port on the RT-AC68U in the AP mode will have lower performance than the remaining LAN ports?
2. What is the minimum ASUS router anyone would recommend for the 2 new routers (they only need at least 3 LAN ports each).
3. Should I plan on running Merlin on the new ASUS routers as well?

Any comments on other options, pros & cons are most welcome!
Thanks in advance for any feedback.

 

[ColinTaylor]

1. Is that true that the WAN port used as a LAN port on the RT-AC68U in the AP mode will have lower performance than the remaining LAN ports?

No.

 

[Tech9]

Any comments on other options, pros & cons are most welcome!

For a brand new system and Ethernet infrastructure available I wouldn't invest in AiMesh at all. What's the budget and location?