So additional ax86u’s will provide more range and throughput vs ax68u and ax86s, correct?Additional RT-AX86Us will be most useful if you can connect them via their 2.5GbE Ports for wired backhaul.
I use a couple of the QNAP QSW-1105-5T 5-Port Unmanaged 2.5GbE switches over Cat5E (100' run) cable and have no hiccups or slowdowns with my 1Gbps symmetrical up/down connection and any concurrent LAN usage (including to 2x QNAP 2.5GbE capable NAS').
Be sure you locate the routers as physically far apart as possible, for maximum performance and coverage. And be sure to manually select the Control Channel that works ideally for the new environment too.
AiMesh Ideal Placement