No, your clients and collaborators are free to invite to your projects as long as they are in the collaborator role within your project. If you want to add additional Project Owners to your project, they will be considered a paid seat.
You will pay for yourself and your company team members as you add them to your workspace. After you have completed the home build, you can send a digital record of your Digs project with all documentation and specifications to the new homeowner as part of the homeowner handoff.