@evensteven 

Hey

Welcome to Omada WiFi!

hopefully some answer for you mate

Here are my considerations:

• Usable AX 5GHz coverage in every room

Sounds like a good idea

• Functioning roaming for devices (iphone 12, iphone 13, macbook pro 2015, macbook air 2021, HP gen 9 laptop pc wifiAC, Bose Portable Smart Speaker wifiAC)

Cant see that being an issue, long as you have some controller online it should work

• Minimize channel overlap (set different channels on each AP?)

With just 2 APs, its unlikely any real issue tbh.   Personally I would just let the controller handle the channels unless you have massive neighbour interference

• Consider reducing signal beyond my house walls (not sharing/disturbing neighbours)

Wouldnt be wasting your time tbh.   That is what channels are for after all.  Their WiFi should see yours and avoid it, also by the time your signal gets inside their house its likely -70db or more so its dead air anyways.   yes, they will see it, but cause no problems at the that signal level.

Questions

• Do I turn off 2.4GHZ altogether?

Hard one..  If all your devices are 5ghz then perhaps.  However from experience most IOT stuff is still 2.4ghz so its a necessary evil.   Personally, just leave it on and auto channel.

• Do I maximise transmission on the AP in the living room and only use this one AP

no.   max power can be negative, its not always the best answer.  As you increase power, it affects closer range devices as it floods them so anything locally (living room) may be affected.  quantity of AP is ALWAYS better than one blaster.  Generally let the controller handle power, its not something you really need to fiddle with.

• Do I buy multiple access points and reduce their transmission power and scatter them across all rooms to localize wifi access and split them up in channels? Pros/Cons?

Leave power on Auto, thats what the controller is for.  It will tweak and adjust power to suit the airspace.  Remember the same airspace can change daily so let the controller control.    Multiple APs is always the best option tbh.

• Power consumtion matters - the less Watt the better (electricity is expensive in Australia!) 

APs pull around 7-9watts per hour so really low power.   Honestly you would barely notice them on your bill.  If however it is a concern, POE Omada switch may be your answer.  Once you get one of those you can set the APs to power off (switch of port) at nighttime etc.