A: You can do so directly in the portal if you have the proper access rights. Please see where to find the section in this GIF:
You can also directly access user management if logged in and authorised here:
A: There is no limit on number of seats or users in the parcelLab Portal. Just go nuts with it.
A: Yes. parcelLab supports Google's G Suite SSO and Microsoft Azure AD via OAuth2.0.