It's obvious from your art that you've already come a long way, great job!
To me, Bob Szesnat has some good points regarding the underlying shapes.
You say yourself you might rush past laying the groundwork a little, but who doesn't
All the work that you've put down into rendering skills etc is going to make you level up all that faster once you put work into the basics.
My experience the last ten years comes primarily from making art in the games industry, so my caricature skills are lacking, however I think it's the same principles that apply for most artists.
These are my five cents:
Draw a lot (duh... But let me elaborate a little)
On one hand, quality practice (really thinking about perspective, looking up anatomy that you have problems with, maybe following some good tutorial) is better than doodling while you're on the phone, but that doodling still is better than not drawing!
When reading books/looking at tutorials, my experience has been that looking at someone else drawing/painting is good for picking up certain techniques or workflows, but it can never replace working with the basics (perspective, perspective! I really like Scott Robertson's book "How to Draw", and if Proko follows the Watts course structure, I'm sure he has some amazing stuff about that as well).
The reason all the really great artists are great is IMHO all the knowledge that lies beneath technique. They could probably create as compelling images with other mediums and techniques.
I have for sure wasted waaaay too many hours watching tutorials, when I could have focused on more important things to further my art.
I hope any of this makes sense.
Personally, I find the tutorials and books about the basics are the ones I re-read every other year or so and really learn something new from every time because the stuff I learnt before matured...