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I think the big thick circle is getting in your way, you only need the guide briefly so I'd make it thinner/lighter or erase it when you start adding features. I would also give yourself more space to work with, by working with a thinner line more zoomed in, (I normally work traditionally so IDK), I'd also recommend looking at a set up tutorial for the software you are using for the type of drawings you are doing, I would find it really difficult to place guidelines and details using the thick, opaque brush you are using right now. 

You've said you are doing 20 minute drawing but I find the class mode a lot more useful, it slowly warms you up into doing longer and longer drawings. 

Keeps going and I hope this helps! x

The characters are all quite expressive, but I think in profile a straiter face line would give a more accurate face shape.

Great sense of motion and movement. One area you can work on is your form quality. Many of the facial features you have drawn don't curve with the subtle plane shifts of the face, but rather feel more like symbols of the features. Though you'd like to be less stiff, don't be afraid to take some time to focus on one facial feature for your drawing sessions so you can really understand the nuances.