I've made a lot of these mistake when I was first writing, I'm still new at writing(only really finished my first book),but I wanted to use advice my teacher gave me.
1:I did this very often, I've now learned how to execute this better, I mostly just left that stuff at the end and even then when I had a character who died a bit early on when introduced; I still wanted to give them some sort of character.
2: I still feel I struggle with this a little, I mainly try to describe the character,environment,etc. I feel the main issue I struggle with is body language. Mainly when characters are performing certain actions.
3: This is also a somewhat issue I also face, but it's mainly due to how well the viewer will relate to how the character talks and their actions.
4:This is something I really didn't focus on, in my next project this is my main focus. Hopefully that can be used as a good steeping stone.
This advice is really useful, I'll make sure to keep note of it