I would simply break down learning how to draw in three stages. Progressing each in order. 1) Observational drawing 2) Perspective drawing 3) Force drawing within those stages, I will break them down even further. I will keep breaking them down until I reach a simple task to master. Then I will go on to the next simple task. This creates a hierarchy. This allows me to focus on small task throughout the day while still keeping the bigger goal. When I break down the task, they are generally already done by the person your learning from. So take advantage of that. The process is never linear, but to have a map like this keeps you on track and motivates you by seeing your progress. EX. Observational Drawing 1) block-ins (then I break it down even further) - Tracing ( you can break this one down even further as well ) - Sight size -Measuring 2) Rendering -2 values -5 values etc. Hopefully you get the idea. I will also add a crucial advice to notice your weaknesses when doing these task. Whatever your weak at must be given your full focus. Those are the ones you must intensely focus in your practice

I didn't check the other two but here I did find perspective errors. In the photo the Horizon Line is far below the page. Your Vps never reach that low. In the drawing the blue lines keep intersecting each other. Make sure both the left and right VPs converge at the same HL. Also in the photo, the green lines are converging upwards. Yours green lines are parallel. I don't know if you already do this but practice measuring two angles that are far apart from each other. this will give you the convergence of the VP. Extend those lines to see where they intersect. If the VPs are off the page like this one, just guess based on their convergence. You can then just put the other lines in between. Hopefully that makes sense. If not I can provide an example.

It is in 5pt. This is free-handed so the perspective isn't perfect. That might be why it's confusing you. Also the Vanishing Points are off the page. Only the center VP is on screen.

Simplify the car into boxes. That would let you understand the perspective better. The one on the right is not fully following the sphere. And if it was it would look very weird. Do boxes first. Then construct the car from there.

If you're not feeling any pain when working out at the gym, then you're not making any progress. I struggled a lot with this too and to me there are two main reasons why. First was my lack of consistency. Some days I would draw and most days I would not because I didn't feel prepared. Drawing everyday keeps the skill more consistent. Second is to learn to enjoy the pain like working out. I still struggle with this but I've made a lot of progress by learning to move towards pain. I also really enjoyed this video on YouTube about motivational styles. It helped me explain the moments I was productive. It might help you too. https://www.youtube.com/watch?v=tRWX21lW_bU Furthermore, it is not the time spent that makes a master but the intensity of your focus.

Are you familiar with Scott Robertson's "How to Render' book? He teaches you exactly this. His Gnomon rendering videos are good too and I think you can also buy it on Amazon? Besides that, I recommend to focus more on drawing than shading. Once you read his book I think you'll understand why. Drawing is a prerequisite skill you need in order to construct the methods for rendering.

I’m pretty sure the distance between vanishing points should always stay the same. There’s a gif on Draw a Box that explains this https://drawabox.com/lesson/1/17/rotation (it’s a rotating box, where you can see the vanishing points moving with the box). I think the distance needs to remain the same or else it would be like using different camera lenses. For example, if you take a picture using a wider lens (the objects look more distorted), take a picture using a long lens and try to put them together, it’s very obvious there not part of the same picture (moderndayjames explains lenses briefly in one of his videos: https://www.youtube.com/watch?v=2XF5YuAK63I , about 4 minutes into the video). I tried to illustrate this using your example number 2, but more extreme. In my example, the green boxes look like they could be in the same scene and the blue boxes look like they could be in a different scene together. But together, the green and blue boxes have very different levels of distortions (because the vanishing points are not the same distance apart) so they don’t work together and make things look weird. Basically the lens stays the same, so the distance between the vanishing points stay the same. Hope this will be of some help! (ps I’m not sure if this is the best way to explain it, or if my explanation is 100% correct, but I’ve heard a lot of people who have much more experience talk about how the distance between vanishing points stays the same in a scene)

Both are wrong, that's not how perspective works. Boxes with the same orientation will share the same Vps. Remember, parallel lines converge at the same Vanishing point in perspective. If you are trying to rotate a box, then No the length for the VPs do not stay the same for each rotated box. I suggest looking at Scott Robertson "How to Draw" page 25. The two vanishing points for a box should meet at 90 degrees on the Station Point. You rotate that 90 from the station point to rotate a box. The VPs for the rotated box will vary in length due to basic common sense geometry. You'll get it when you see it. hope this helps.

I suggest to draw in the station point. It will help you place the vanishing points and Cone of Vision properly instead of just guessing them. I find it difficult to explain without showing you. If you have Scott Robertson's book "How to Draw" I suggest to look at page 24-25 specifically. Also about that table, the book "Framed Perspective Vol.1" page 56 shows how to construct a table. hope this helps.