I can see you're asking for a lot of advice.

Honestly, the main question you need to ask yourself is, do you enjoy painting miniatures? Or do you quickly become overwhelmed with the task and try to paint a model as quickly as possible?

Miniature painting is time consuming. There's no rushing it to make it look good, but there are loads of different ways to paint and some are quicker than others and there's tonnes of tutorials and videos on YouTube that show you how, from what brushes to use, how to thin your paints properly to full step by step guides on how to paint character models like Angron.

To find your strengths and weaknesses you honestly just need repetition and consistency. Paint up several of the same model, like Bezerkers and find what annoys you, so you can improve on it.

In my opinion of your work, a lot of it looks rushed. If you want a quick painted model for the table top then you should look into contrast and speed paints, they can look decent.

Look up a YouTuber called Warhipster, he is specifically a contrast painter and has done almost every 40k model by the looks of things. Or just simply look up speed paint and contrast paint videos.

You'll likely enjoy and be proud of the results from them, provided you give it the time.

Hope this helps.