We recommend you take the beginners track series (at least) four times (meaning for four months) to give you a chance to take all four different topics covered in each of those months, as well as getting a good foundation with your basic send-out, swing-out, lindy circle and charleston.
After four months, depending on your comfort level, you can choose to take another round of beginners track series, graduate to Social Dancers and Technical, or take both classes for a while. There is always something more to learn in either of the classes, and there are no exams :)
If you are hesitating between beginners and Balboa series, we advise you to take beginners first and come back to Balboa later. It is beneficial to have some Lindy fundamentals when taking the Balboa series.