You can install it directly from their GitHub repo or through Obtanium.

Go to your browser settings and to the Search section. There will be somewhere in there to add a new search engine. Add in 'https://noai.duckduckgo.com/?q=%25s' then set it as your default.

You should be able to do the same if you're using a search widget directly from your launcher as well.

Definitely Zigbee or Z-wave instead of wifi. Once you start to build out more devices you will be glad to not have gone down the wifi route.

I went with Zigbee and have Sonoff SNZB-02 temperature and humidity sensors in each room that have been absolutely flawless since the day I installed them, and they last about two years on a single battery!

I would obviously recommend them but I don't have any experience of other thermostats or of Z-wave.

I did also install smart Zigbee TRVs on each radiator but I don't rely on the internal thermostats of them as they don't accurately represents the overall room temperature.

As others have mentioned the Philips bulbs are about as good as you can get but they are also the most expensive. And that you can save money by going with the IKEA lineup but the quality isn't as good. But your third option is Innr bulbs which sit perfectly in between Philips and IKEA for quality and price.

TLDR

Philips - best quality / most expensive

Innr - medium quality / middle pricing

IKEA - lowest quality / least expensive

Note: when I say the IKEA is the lowest quality, I just mean between these three. They are still miles ahead of any of the no-name brand crap you can get on Amazon.

I use Syncthing for files/photos/videos and Nextcloud for calendar and contacts.

Amazfit with Gadgetbridge.

I bought one a couple of years ago and it works great. Gadgetbridge keeps all the smart functionality local to your phone.

I've heard good things about the Garmins as well which I think are mostly also supported in Gadgetbridge.

Yeah, just use the Beta, it's extremely stable. Don't get it from the Play Store though, as you've seen it hasn't been updated in years. Just get it from their GitHub.

I've tried quite a few after leaving Nova a few years ago and have settled on Lawnchair. It seems to be the most stable and is under active development.