Hey Marco,
Welcome!! I'm fairly new to Quantopian as well (active since early this year) and it's been a steep, but fun, learning curve. Here are some suggestions based on my own experience:
Python:
I too watched and used the cloned notebook in Lesson 2 (intro to Python and Jupyter) but I had to take some additional courses on Udemy and Datacamp in order to get the foundation. There's a ton of free Python lessons on YouTube as well though, which may be more than enough for you if you're already familiar with R. The YouTube course I've linked to is the one I found most useful, and it's the same guy from Sentdex (Harrison I believe his name is) that does Tutorial #3, and there's a bit of overlap there (looks like it's similar or same as the Forum tutorials you've linked to above).
Once you have a good foundation in Python I'd look at getting a good understanding of Pandas and Numpy as well (I'm slowly getting there as well).
Tutorials:
These are all great in my view. Once you have a basic understanding of Python and are comfortable with Jupyter notebooks, I'd start doing these in order. Maybe skip Tutorial #4 unless you're eager to dive in to trading Futures right away. Watch the videos and follow along in your own cloned notebooks, changing some of the code/parameters etc. to see what happens.
That should keep you busy for a while. :) Once you've done all the tutorials, you may want to start looking at some of the lectures, though they tend to be quite advanced (for me anyway). Perhaps look at the Factor Analysis lesson (and start using Alphalens and get familiar with using it), and the Long/Short Equity lesson, and any of the pre-requisite lessons.
The FAQ I hardly look at much anymore, but I believe I did find it quite useful early on.
I'd also recommend having a tab open with the API help doc page, and search it with Ctrl +f whenever needed. I find the documentation usually pretty good and helpful. Also, ask questions in the forum if you get stuck. There are a number of very helpful people on here (just don't expect others to always do the dirty work for you ;)).
Lastly, I'd check out this excellent 6 part podcast series with Chat With Traders and Quantopian. All of them are super good, but if you're interested in Q's (possibly over-/mis-) usage of the word API, check out episode #4 with Trading Systems Engineer legend Scott Sanderson.
Best of luck, and see you in the forums!