New Skill Tree Strategy
Is it better to do all the levels of each section before moving on, or do the whole tree at level 1 and then start again from the top?
I think there are a number of factors to consider. For complete beginner learners, I don't think taking any lessons just to Level 1 is sufficient to have learnt the lesson, for more advanced users or perhaps people with prior knowledge of the language it might well be.
So ultimately you have to decide yourself, what your level of knowledge is and how well you feel you've learnt the lesson as to whether to stop at level 1 or keep practising up the levels.
I wouldn't recommend a completely new language learner to take each Lesson to level 1 and keep going down the tree.
I'm studying Mandarin, so YMMV with this.
I started by attaining level 1 on each topic in a section before moving on to the next section, but I soon found by the end of the second and beginning of the third section, I was having trouble remembering words I learned earlier that were fundamental to the new lessons. So I decided to go back and level up each to level 3 before moving on. That helped, but still wasn't enough for some of the topics. Now I am leveling up to five before moving on with each topic. It can be pretty boring doing this, but so far that change has helped quite a bit for me. When a character is reintroduced in a later lesson, I instantly know it now, whereas before I would have to think a long time on it or get the question wrong.
I suspect other languages might be easier to skip ahead, especially if they have an alphabet like English, making it easier to guess the pronunciation, and you can guess the meaning of the word by its root, etc. In Mandarin, you aren't really able to divine the meaning of 汉字(Hànzì - Chinese Characters) by just looking at them (at least, I don't know how to do that). I have to commit them to memory. So for me, leveling each topic to level 5 to ensure they are permanently in my brain before moving on is the best way to go.