A link speed of 950/500 Mbps requires a router with a fast CPU (x86_64 or ARM), see the benchmarks.
When the provider's equipment suffers from bufferbloat, deploying SQM can improve the latency under load, but raises the CPU demand further.
Using separate devices for the router and WiFi access point is probably a good idea here.
WiFi speed for far away users can be optimized by installing additional AP's closer to the users, preferably connected to the main router via wired ethernet.
I do not own any recent Asus router. In addition to the brand, I would also consider OpenWrt support, the hardware specs (SoC performance, WiFi speed and drivers, Flash and RAM size), availability (new or used) and price.
The additional radio is useful for the backhaul when you cannot install a cable.
Tri-band APs improve the overall throughput when the backhaul is wireless (mesh or not).
With a wired backhaul, which I recommend, consider increasing the number of APs instead of using tri-band devices. This gives you more flexibility in their placement such that each client is near an AP and gets high data rates.
I don't use a wireless mesh network myself. As I understand it, three or more APs maintain wireless links among each other and figure out the best route for the data packets. Where the best route is obvious, such as with 2 APs only, or with 3 APs in a linear constellation, you can just set up the links manually, and mesh does not provide much advantage.
Some vendors use a central controller to manage access points and call that "mesh". This can be a useful feature even when the APs are connected with cables, but will only work among devices from the same vendor, and only with vendor firmware.