Yes, you make an account on the new instance but then you can add your original account as a moderator/admin. But beware! If the instance is on 0.17.4 or earlier, and you edit the display name with the remote account, the community will become undiscoverable. It’s a glitch that was fixed in 0.18. Most instances will be on 0.18.1 soon enough so this won’t be an issue for long. Just something to know about.

No. You’d need to register an account on that instance to create a community there.