With regards to air quality I can highly recommend the luftdaten.info project. I wrote up how I built my own sensor and integrated it into HA. I live in Sydney and this sensor has turned out to be extremely useful over the last couple of weeks.
How much did this cost you to make? Looks interesting. I have an official NSW station about 1km from here, but I’d like to have another just to compare.
I’d estimate about AU$60 in total. $30 for the air quality sensor, $5 for the temperature sensor and $10 for the ESP - all from China. And then about $15 for the case parts from Bunnings.
If you have never done any such project you may need to add $10 more for sundries. I still had stuff like cables, connectors, plastic mesh, plastic tube from previous projects.
Looks like NSW uses the AQI form of air quality measurement, easiest way to do that would be via the built-in WAQI component. Personally for me in Melbourne I went straight to the Vic EPA since they moved on from the AQI method in 2019.