Im currently using unifi provided dlink dir825m router. I have also bought another 1 of the same model to create a mesh setup. So i currently have 2 units using in a double story house.

Currently with the 2 dir825m routers, my setup is (@30mbps)
1 pc on lan
4 wifi cctv
when return home, 1 tablet, 2 smartphone on wifi. and the occasional smart tv on wifi.

Not much complaints with the current setup, occasionally slow speeds and sometimes cctv responds abit slowly.

I'm planning to move to a corner house mid next year, with intention of using 8cctv.

My question is currently wifi5 mu-mimo is max at 4 devices. does my current mesh system with 2 routers provide 2x4 max devices? or is it still just 4 devices throughout the mesh network.

I initially plan to add another dir825m router bringing the mest up to 3 points. But was wondering how well it can handle 8cctv at once + additional devices. Or should I start considering a new setup with wifi6? since wifi 6 mu-mimo is up to 12 devices. However i doubt my current cctvs (EZVIZ C3W) is compatible with wifi 6 features.

I may also consider upgrading to the 100mbps plan once i move and am also wondering how well the dir825m may perform.

Thanks in advance for any inputs.

Based on the spec provided on manufacturer website, your current cctv EZVIZ C3W only supports wifi over 2.4GHz and operating them all at once over Wifi will greatly congest your 2.4GHz wifi. Your best bet is to wire up all of your cctv to the DVR if possible.

what if i run my 2.4ghz exclusively for the cctvs only? since most of my smart devices support 5ghz anyway.

i have considered the ezviz x5c dvr but im not sure how well is the coverage if i have cctv both at the front gate and backdoor. (about 80ft cctv to cctv)

You can try.. but wired is still the best solution. Wireless is not guaranteed to work perfectly.