kiwi

Can I only create a community on the instance I joined, or can I also create a community elsewhere?

You can only create a community on the instance you have an account on, but people from other instances will still be able to follow and post to it.

I think that's right. A request for deletion gets made and it's up to each server to decide if they will honor it.

You might be able to save the website as a progressive web app to your home screen?