From your drawings you look like you're on the right track for your anatomy and landmarks. To help with drawing the muscles in these early stages, simplify them down to simple 3d shapes; for example the thighs and the upper arms would be cylinders. Use rhythm lines to tie/link things from side to side to also help give a sense of symmetry and balance in the figure as well. Keep at it Max!

As far as I can see, you already have a solid knowledge about landmarks. I can't seem to find any fault with the landmarks. As for the muscles, since you haven't had a good grasp on the muscles yet, you did the right thing by relying more on the visuals of the reference, and less on the guessing part of your knowledge and imagination. The other thing I will advice you to to look out for is the volume of the torso. Because from what I see from your works, that you still treat the torso as a 2D rectangle rather than a 3D box. This in turn makes the torso look rather flat and thin. Try to draw a box instead of a rectangle when you lay in the general shape of the torso.