Nothing is stopping you from making a new account but there is no account migration. Assuming you and your instance admin arent bad people (as in, your old account isnt deleted or banned) you can make a new account and put a link to your old one in your about me section of your profile.

Everyone you see on the public timeline is on a server that contains at least one person someone om your server follows. Thats how servers get to know each other. If you go seek out and follow someone on madeupname.social and youre the first to do so them you have caused new federation!

Its a good thing. Interract with as many people as you care to and your instance will benefit. This isnt like Reddit where subs will ban you for contributing in any way to subs they dont like. Its just not like that