Check out GrapheneOS! It's built from AOSP with some privacy and security improvements, no change in user experience though. It also removes all the bloated Google crap, as well as the spyware. It's the only mobile OS I would use nowadays.
There are millions of systems still running windows 95 for hardware that can't use anything newer (think CNC machines).
These are never connected to the internet though. Also, these aren't personal devices that store sensitive information, they're just used for one specific task (and without internet connection), which is fine.
Not directly related, but if you ever want to watch YouTube videos on a Chromecast (or any Android TV-based device), check out SmartTube. It completely removes all ads and other annoying stuff and massively improves the experience.
Definitely use some sort of cloud server, I'd stay away from your VPN + port forwarding idea, it will only cause you issues. I heard good things about WooCommerce, it's FOSS. You can't get around JavaScript, it's impossible to build a functioning online store without some kind of JS. WooCommerce doesn't include trackers though, just the bare-minimum JavaScript that is required for the site to work.
I occasionally use ChatGPT, I don't find it that useful though. I mostly use it to summarize long text, etc. I also like Phind, which can be used without creating an account. I would never pay for AI.
Revolt will be perfect for you it perfectly mimics the Discord UI/UX, and you don't need E2EE if you are in control of the server