So, I've been playing. And playing... :D As I wrote and planned earlier, I did the 2-3 books per day or week, but that didn't work out as efficiently as I wanted. In March our trainer Leena gave a Very Good advice.
Play the first piece of each book. Then the second. Then third. And so on. Of course book 1 has most pieces (17) so the others rotate more, but that's only good as they are more demanding.
It really works! At least for me. One doesn't get bored so easily.