I've successfully completed the AST's BBST Foundations course, and a couple of colleagues have just completed it (and enjoyed it!).
It is possible to self-study with the material, but I'd definitely recommend doing the AST course if you can. (There is a self-study student workbook in preparation, due out late 2012/early 2013). When you do the AST course, you'll find yourself working through the material supported by peers and tutors, with lots of supporting exercises and quizzes. You'll find yourself responding to the new material you've learnt as part of the exercises, but you'll also find that you're expected to review and comment on other students' responses, consider their feedback to you, and then decide whether you'd modify your original answer. I found that this process gave me a much deeper appreciation of the material - it really forced me to examine my ideas quite closely, and rethink them in many cases.
It's pretty intense. You pretty much get out of Foundations what you put into it in terms of time - the course recommends 12-14 hours a week, and you do need to put at least that much time in (some people put in much more, but it's doable with that time). I'd recommend taking a look at http://www.associationforsoftwaretesting.org/training/orientation/students/ as it'll give you a good idea of what will be expected of you.
As might be obvious from the above, I think the AST courses are fabulous - both in terms of content, but also in terms of instructional design. It's so clear that every aspect of the course has been carefully thought out to increase how much and how well you learn.
I intend to complete all three courses at some point, for me it's a matter of when I can afford the time. I'd definitely recommend at least doing Foundations to any tester (the experience level on the session I took ranged from a couple of months to more like a couple of decades). The order you suggest is correct - Foundations is a pre-req for Bug Advocacy, and you need to do both Foundations and Bug Advocacy to prepare you for Test Design.
Hopefully I'll see you on one of them sometime? :)
Note: I also found this article by Cem Kaner about the courses - http://www.logigear.com/magazine/articles/black-box-software-testing-test-design-course/