I am building an outdoor kitchen. I already have an exsisting outlet. I have a pool light, low voltage outdoor lights, small refrigerator, a rotisery with light and I want to add a 10 amp 12 volt AC/DC converter to run a outdoor stereo. All will be connected to the exsisting outlet which runs off a 20 amp GFCI breaker. How many outlets can I have?

Outlets don't mean much in themselves, you could have 10. However, what is important is the load you will put on the circuit. Add up the watts of each item, and divide by 120 volts. That will tell you how many Amps you will draw if everything is connected and powered up. Why are you using converter? They are used to change 120-240AC or vs. Do you mean inverter? They change DC to AC. Is it a car stereo?