These look great! I think the contrast is good and you can really tell the light source.

I'd say try to add lighting and shadow to the background like your reference. It might help with the figure in the far back.

First of all, DAAAAAAAAAAAAMMMMMMN! This is aesthetic. I think the side values for the tall skinny figure could be lighter, but overall everything works so well together. Love it, so much progress here.

The following is hella long, so here's a summary: Keep studying as much as you can, do study challenges but make a theme and infuse some creativity into it. As your studies get more complicated the easier it will be to do illustrations. Each of the videos/topics here are like tools, so if you try to tackle something you might get frustrated because you don't have all the tools yet to finish the job. Also, focus on the research and process rather than the finished product.

tldr;
For your other question I'll give my experience and you can take what you want from it.
One big thing I learned from doing the later terms and the design course from CGMA is: I was being too ambitious and diving in head first to my personal projects. So much thought needs to go into the shape of things, the style that you want everything to be in, which reference material you want to use etc. When I did personal projects in the past I felt discouraged and gave up on a few. When I did finish something I would share it but the feedback was even more discouraging because I was lacking in so many fundamentals.

One thing I noticed was that I got more satisfaction from modifying studies or doing challenges where the focus was practicing something but I added an element to make it fun.
When I did Inktober a few years ago, I decided to practice anatomy so I treated my Inktober drawings as figure studies and made it fun by adding clothes based on the themes.
I finished the challenge and I'm really proud of it, despite not liking every design lol.

Another thing I noticed is that focusing more on the process and research makes me put less emphasis on the art techniques and makes everything more enjoyable. I think I used to worry too much about the textures, anatomy, etc and that crippled my creativity. Before I knew it I got turned off from what I was doing and gave up (ie that 2-d city project I was doing ) But when I started to be okay with ugly scribbles at the beginning of the process and focused more on how things work and shape language of my ideas it became easier to draw more finished things.

I think it's good to be study and research focused at all times and have fun with it. Once I started studying more advanced topics it was easier to do more advanced images. Now I feel more confident with tackling character art, props, and general illustrations.

One concrete example is the whole "what should I do for the background?" phenomenon that plagues most of us artists. Before, I used to think of a cool character, draw the skeleton, pile on the details, and put some generic gradient in the back or "suggest" a street or room etc.
Now going into my personal project I wrote out characters that I want to focus on and listed characteristics for them. Then I went and gathered photo references for the general feel of each character and the world they live in. After that I looked up art that sums up the general style I want the project to be in. (I promise I'm getting to backgrounds, stay with me )

From this point on, once I get the character sheets down, I will have a ton of information to construct an illustration. I can tell myself "Okay, this character has this personality and would stand like this. They have this kind of role and live in this time period so they'd most likely be in this location." After that it's a matter of making composition thumbnails and bam, I have a full scene instead of a random character with a bokeh background.
On top of that, I'm so hyped from the inspirational references and art I collected that it will be hard for me to abandon it. I'm excited to see how everything turns out.

Sorry this is so long, but I hope it helps you in some way

This looks amazing! Your value knowledge is really shining here!

The main things that sticks out to me are the front plane of the forehead and the back of the head. The forehead's front plane is pushed forward too far and a little too curved. The back of the head is too rounded and pulled back a little.

Keep up the awesome work!

That is a really good exercise! Haven't seen many people do it actually. Getting to know the head planes is probably the number one pitfall for many artists.
You did really good with shading, I can only point out one issue: the plane on the cheekbone facing up should probably be lit the strongest as well as the upward-facing plane above the lips. I presume the light on your source photo is still slightly above the head (judging by forehead and eyelid ligting).