Since you're a software engineer, I'd say get a mini PC. More resources that will allow more tinkering. Do you want to use HAOS with apps (add-ons)? I personally (and I'm an E&E/software engineer myself) run HA Container, because I then still have access to the host OS.
Be very careful with AQ sensors: the best ones are expensive and split responsibilities. There are some excellent posts here on the topic. I've always wanted some, but I don't have personal experience with this. I've looked at Airgradient before and it seems to be of decent quality.