Connieeee, way to go on your 5 minute faces and expressions, that's very good graphic shapes and lines, and spaces, too!
If I was to give you some totally honest and sincere advice, it would be this: Here:
I love the silhouettes and how organically they read as the outlines of your heads, but I think they're they're, still, I really don't feel like there is enough cartooniness in the faces. Would you please push these positive shapes, and pull those negative spaces?? Why don't you please loosen up and liven up those facial expressions, with 30 minutes of 2 minute drawings? (15 2 minute expression drawings)
The reason why you could do these critiques is because, it can, shall, and will be able to develop and refine your eye for design, and to help your current goal. If it's to help improve and caricature my perception of spaces on my faces and head angles, then I suggest, allow, and encourage you to go ahead with it.
For more information on how to quick sketch your heads and facial features, then please check out this video.
https://youtu.be/wAOldLWIDSM
Cheers to you, Connie!