CFK
Here is a link to the latest discussion about AoPS books and courses:
*** Link no longer working ***

To answer your questions: DS13 is currently in Intro to Number Theory. This is his third or fourth class from AoPS. You (and your child) learn how to approach AoPS as you go. Of course the more you put in, the more you get out of it.
In my son's case, he absolutely has to attend the class, reading from transcript is just reading, if you know what I mean smile
AoPS class meets once a week for an hour and half. Your child will get the most out of the class if he/she participates in an online discussion/solves or attempts to solve problems that are posted by the instructor. To do this you not only have to have a good grasp of the subject (they ask that you prepare by reading the assigned chapter), but you also need to type fast and accurate. Using LaTex is a nice bonus but it is by no means necessary. Your child will learn LaTex as he goes along.
I would not worry about too much repetition, it most likely is not going to be a problem wink
After each lesson an instructor posts online problems, generally about 10 of them per week. They are not necessarily based on the material covered during the lesson, sometimes they go ahead (Ghost is not able to solve many of them initially but has no problems a week or two later). There are also so called "challenge sets", 2 or 3 of them(between 15-20 problems each), depending on the class, that are evaluated but not graded.
Time wise it is very challenging for my DS13, as it is done outside of his regular school and other EC activities.
I wonder what Cym will say here, but I honestly believe that an hour a day (meaning 7 hours a week) at least is needed to be able to complete posted problems and the challenge sets. At least, sometimes more.
As I have indicated before, IMO AoPS is for mathy kids. The problems are difficult because 90% of them go outside of the book. This is problem solving/contest mathematics, not so much regular school curriculum.
Also, remember that you are taking this class in the evening and at home. Not the best environement to stay focused. As we go along I have figured out ways for Ghost to stay focused and involved, but it did take some time .
Ghost is not able to take Algebra class that is starting in June, but I do hope they will have another one available in the fall. We have already agreed in our house that he is going to do Intro to Algebra followed by Intro to Geometry, even though he will be in Pre-Calc next year.