Hey Mario,
welcome to the community =). In terms of proportions I don't see any issues. Only thing I'd try to work on is linequality, It is a bit scratchy at times and it also feels like the image-resolution is a bit to loo low, because the line looks like it has a thickness of 1 pixel.
As for the progression, it depends a lot on what your goals are and what your focus is. In general, my oppinion is that you should have at least done the assignements and should be somewhat comfortable doing them. Frequent feedback will also help knowing if there are problems with your works. That being said, if you feel like you get bored by the exercises it might be worthwhile to take a peek at the later assignements and come back to the current ones later.