I do as much as my brain can hold at one time until I realize I've reached my limit. Then I know in my case, for example, that beyond Lower Intermediate I shouldn't even bother with right now.
So, do as much as you can. When it gets overwhelming, back off. And note where your limit is.
I personally think you should focus on one section at a time since the lessons build upon each other in each section(Newbie or Beginner, I'm planning to do beginner after Newbie just so I don't miss any important vocabulary before going to Lower intermediate.)). I don't recommend trying too hard because the knowledge dissappears quickly. At first you can handle a few lessons a day but as Peter-san say, it's better to start Kanji as soon as possible so I learn every single vocab and Kanji in detail and take 1 lesson a day with a review of six lessons once a week.