If I already own a domain name, do I have to pay to transfer it to Robert Maxim's management when I subscribe to your website service?
You are in no way required to transfer or give up control of your domain.
Robert Maxim can manage your domain if you like. Often our clients transfer domain administration to Robert Maxim for convenience. Your domain ownership always remains yours. We only administer or manage your domain.
If you are comfortable managing your own domain you can set it to point to your website on our web servers. You will need to ask your domain registrar for assistance with this.