Why are you assuming that you will become the bottleneck? Have you talked to your employer about going part-time or getting some flexibility in your hours? If you are a valued employee, your employer may be willing to work with you to keep you on payroll as long as possible. What options are available to you (hiring someone part-time, etc) before you make the leap?

If you truly believe in what you are doing, you are committed to it and have the savings to take care of your expenses while you are getting established then jumping into it full-time may be the right decision. If you are going be awake at night second guessing yourself then maybe not.