I'm not sure if there's some special calling feature to reach a previously associated provider, but when I've been in that situation I just borrowed my roommate's phone.
Yes, it is possible. You use whatever the provider's method is to download an eSIM to that device. Usually it's logging into their app or calling their support to register the IMEI or whatever.
In the store if you're getting the phone from a store, or somewhere with wifi (home, a friend's, a cafe) if you've gotten it some other way.
If you don't have any of those, you probably live way out in the jungle, and I'd be surprised if you had service even if you got the eSIM. But in the edge case that you somehow got home delivery postal service in the jungle, you'd probably be able to survive just fine without it until your next trip into town.
In the extreme edge case that you are in the jungle, get service, and your need is critical, I would have an activated backup phone tested periodically and ready to go.
Depends on the phone. The newest ones let you use multiple ones simultaneously, one for calls/texts and one for data, for example. Slightly older ones only let you use one at a time, but they let you activate and deactivate multiple downloaded eSIMs.
Yes, especially in the UK, since they're a surveillance state.
There are some things that will always get flagged on any platform. This, drugs, and connections to sanctioned countries, for example. I've heard of people in the US having their Venmo accounts suspended because they put "Havana" in the transaction description. Havana is a local dance club.
What are you running your containers on? I just put my VPN on the docker host so I could be sure I could use the firewall to block traffic from going out except over the VPN.
I have no idea what CMUS are but you can check previous bug reports, or just open a bug report and ask what they'd like to see.