You can create a Stebby Service Provider account while being in your personal account by clicking on your name at the top right and then "Create new group". From that point of view, you can always change the role in the future, because when you log in to Stebby, you are first in your personal account.
Joining the Stebby environment is always free.
There is no monthly fee for Standard Package Service Providers. For Basic, Bronze, SIlver and Gold packages, the service fee is applied according to the agreed service fee percentage. More detailed information in the packages description.