I went through all of the beginning lessons before doing any others (except newbie and survival phrases). If you study each one until you can fully understand it (reading the PDFs really helps with this), you should have a pretty solid grammar base for moving on to beginner season 2. You'll find that BS2 is more of a review with a few extra useful bits thrown in, so they shouldn't take as long to go through, and then you will be ready for lower intermediate.
I followed this pattern and found I made good progress, and I'm halfway through the intermediate lessons now. I think as long as you study the lessons until you understand them fully, they are never really above you. If you don't understand a thing at first, it just means you get to learn more from that lesson.
I'd recommend some "external" reading to help build up your vocabulary and solidify your understanding of the grammar. I've made a lot of progress with my reading since I bought some manga and children's books. Also, another source of listening practice, such as TV shows, radio, etc, is very beneficial (assuming you don't do these things already).
It might seem like you're going to fast, but as long as you read the PDFs and fully understand each lesson, you are on the track to success. I only started studying in February, yet somehow I was able to read my friend's e-mail yesterday without Rikaichan -- never underestimate the power of jpod