I have been admiring this project for a long time and have wanted to start using it - however, I have to admit that between my family and job, I just don't have - and probably won't have the time to do it.
So, I declare defeat and am happy to donate the devices that I have been hoarding for this:
1x Google Onhub (TP Link version)
3x Google Wifi (the version with USB-C connectors).
I am pretty sure I have all required power adapters.
The devices are currently in Switzerland, and I am happy to mail them inside of Switzerland. For outside of Switzerland, I'd need to figure out shipping etc.
You picked hardware that is supported (at least the onhub, I'm not up to speed with the different google wifi variants), but which is on the more complex spectrum for the initial flashing (but once you've done that, it should be relatively straight forward).
The main issues with this hardware are probably less on the OpenWrt side of things, but more with getting beyond google's walled garden (switching to developer mode, etc.) and installing OpenWrt in the first place.