S4B to Teams - enable or migrate?

1) If you don't want to setup an hybrid I guess the process would be that you first disable all Skype users , make sure all Skype attributes are gone in Active Directory, start syncing with AAD and then enable users in Teams. Then you can uninstall Skype servers. I don't recommend this and never tried it since it is easy to setup and hybrid and move users.

2) Yes, you can remove the Skype hybrid after you moved all your users to Teams. You can also remove Exchange servers if you want to, depending on your setup they might be needed.

I would recommend you to setup a hybrid for Skype since you don't need to rush the move of the users and they will be able to keep their contact lists.