As the name suggests, a freelance copywriter is not attached to any one company on a long-term full-time basis. Instead, a freelance copywriter will function as a consultant and can have multiple clients at a time. This gives you a lot of power to determine your workload and decide when you want to work or not. If you do decide to have multiple clients, you will need to organize your time efficiently so that each client gets an adequate amount of your attention.
Because you are a freelancer, you will find yourself using your resume more than most other professionals. Ensure that you clearly state the value addition of your work to previous clients in your resume. You will also want to list the kinds of copies you have produced in the past so that future clients can get a good idea of the work you offer.