My current job gives us a laptop with Ubuntu, but allows us to, at our own risk, install whatever OS we like. I recently turned down an offer primarily due to Windows being required (PHP and C# shop).
Kind of makes sense - casting is usually a webstream without extra dev effort. I'm not sure if you still can, but I used to circumvent twitch ads by casting from my phone. Not to excuse their shitty behaviour; I gave up on them years ago and started hosting my own content.
I installed this same system a few months ago. It's been fantastic - responsive and intuitive. The 5V pin in the CN105 connector means no external power or wiring is required. We haven't touched the remote since it was installed.
For Headscale, I don't have any direct experience but unRAID has a decent Wireguard plugin, and should get you up and running in a pinch.
And for your self-hosted services (especially Bitwarden) ensure you're not exposing this on the net, by VPN is the only option I'd recommend. Even so, I prefer to use Bitwarden's hosting with a family plan, for peace of mind and resiliency. It's also much easier for my family.
UnRAID is a great place to start - it allows you to scale cheaply as you need and is easier to fix mistakes. Good luck, and happy homelabbing!
I mean, it's not an option if it's required by law. As to your second point, I have seen news articles talking about "sponsored recommendations", but nothing as blatant as tv/radio ads. https://www.stuff.co.nz/business/360895851/ev-drivers-be-bombarded-incar-adverts