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’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)