Not sure why everybody is upset that it's a separate app. Google has been doing this with Android for almost a decade now in order to bring new functionality without needing to update the entire operating system.
Just being pedantic regarding the AI models; they're only censored on the publicly hosted versions. Like any other model if you run it locally you're only restricted by the model's training
Get a prepaid with an eSIM with AT&T/Rogers (or any of their MVNO's) for maximum compatibility; cheapest the better. You need an eSIM compatible phone. You can verify this through the carrier's site from your phone.
Absolutely. They're nothing alike.