What is the starting salary for a full-time self-employed Dominatrix?

There is no salary. As with most self-employment, you are paid by the clients, at whatever price for the "service" you decide to charge. Since the clients who can pay the most have jobs and cannot use the "service" when they are at work, if you charge a high price, you will only be able to work part time (when the clients/customers with jobs are not at their jobs); to work full time, you would have to charge less (so that clients/customers without jobs can pay).