I selfhost on a cheap VPS I found on LowEndBox. The security setup (not SimpleLogin) was more involved than SimpleLogin. Pretty easy to get working and I’ve had not a single issue in 1.5 years of selfhosting it. I pay $11/yr for the VPS compared to $30/yr for SimpleLogin.
With regard to your specific questions - I’ve only selfhosted for myself with one domain. You can add multiple users and domains though.
Devils advocate, why built more nuclear plants when you could build more renewables? If it’s a scaling issue, in that you need a ton more infrastructure for renewables, and need to supplement with nuclear, wouldn’t that then always be the case in the future? I hear nuclear is needed to bridge the gap often, but it always sounds like it’s temporary, which I don’t understand - seems like nuclear would be needed forever if renewables aren’t able to scale well?