The person who will buy AdminProject access, will become automatically project owner and will have full control over all the parameters, including inviting new users. Owner can designate administrators, they also can invite new users to the project.
You cannot remove the AdminProject logo at the moment. You can use a custom footer that can be uploaded through Settings Upload footer link on the right sidebar. It will be scaled down to fit the space provided.
Create a .docx file using popular office applications like MS Word or LibreOffice Writer. Put all logos and text information in header and footer. Leave the main body of the document empty as this space will be filled with the content from AdminProject.