If you are planning wifi and have acreage, also consider your mesh expanding outside too.
We planned two externally located APs as our facade is stone. Without this you may find things like doorbells, cameras and wifi outdoor plugs struggle real quickly
I’m planning on 5+ Aruba InstantOn APs throughout the house and 1 or 2 outside (all hardwired with Cat6) so wifi should definitely not be an issue.
I’m leaning more towards Meross dimmers now. Do you think the current hardware can support matter/thread via a firmware upgrade?
Ive used these.
Candeo Zigbee LED Dimmer Smart… Amazon.co.uk
Awesome, work well. Ive fitted several to low power singke LED fixtures with no flicker.
However if you need the little resistor, they are also sold on amazon
Their current publicly stated position is that they will release new Matter-compatible devices sometime in the future (they have one Thread smart plug model now), but current WiFi devices, even the ones that work with HomeKit, will NOT be upgraded to work with Matter. So unfortunately the answer to your question is No. 
The US market has so much more 