The one thing I think this is lacking is page flow. The Idea that you should arrange panels in a specific order that mimics the way we read text. The panels' order should be left to right, top to bottom (like the attached image). If you want more practical examples, google "comic page flow" and if you want to go more in-depth, Scott McCloud's Making Comics has a good chapter covering the topic.

Usually, for these kinds of illustrations, you would have to figure out the anatomy based on references you shot with a model (or using yourself as a model). Proko talked about this on the last episode of the draftsman podcast (titled "Developing an Illustration"). There's also info about this in Gurney's book imaginative realism. Are you trying to do this purely from imagination without any reference?

The most consistent problem that I'm noticing is that sometimes the lines in some axis of the box intersect even though it's inconsistent with the suggested vanishing point of the perspective. One thing that I like doing it's drawing the extremes angles in the outer part of the object and then put lines on the middles with "in-between" angles that are just an average of the two extreme angles. it works when doing thumbnails too!

You could start by working on your line confidence. There's a couple of drawabox lessons that teach you exercises for improving your dexterity. https://drawabox.com/ Just do a little bit every day before start drawing, at this stage is more important to build muscle memory over a long period of time instead of trying to solve the issue in a day or two.

I'd like to know if you want to learn character animation or if you want to make animated films. Because if you want to do character animation you'll want to learn the principles of animation, body mechanics, and general workflow. For this people generally recommend books like the animator's survival guide and the illusion of life. On youtube you can find Aaron Blaise and Toniko Pantoja, they usually talk about this stuff. On the other hand, if you want to create shorts, I'd recommend you to start learning how to write and storyboard, picking camera angles that aid in the telling of the story, understanding how to use music and editing to elevate the emotion of a scene, etc. For this, I'd recommend checking these out: https://www.radhowtoclass.com/projects It's not a hard dichotomy but it's good to start with a priority in mind.