We would love to have more active members in the Dâ€™Ooge study group, but as Edonnelly has point it out we are much advanced. We have finished the lesson XXXVI this week.
Although the optimal study speed would depend on a lot of things (free time, natural skills, and so on), in my opinion the one lesson per week that we are doing in the study group is a little too slow (but even that has proved to be too much to must initial members). In my opinion, more then the number of lessons you should (if possible) try to spend an hour per day studying the lessons without doing more then one lesson per day. I found that was, for me, the best method while I was studying alone. That way I retained most of the vocabulary in my memory and the concepts of the lessons could be learned without great troubles.
Of course this in my personal opinion.
Best of luck for your Latin studies.