Does a person need to have an account to see my vaams?
No, you can share your vaams with anyone. The people that you give the link to, will be able to watch the vaam.
Is it possible to change the account I'm logged into?
If you log out from https://vaam.io, you'll be logged out from the extension too.
If I delete my Vaam account, will all my vaams also be deleted?
Yes. If you delete your Vaam account, all your vaams will be deleted.