How many English words does 4000-8000 Chinese characters correspond to? I have to write a grant application in Chinese. I intend to write it in English first, and then get a friend to translate it for me. I am supposed to give an overview of my research project with a word count of 4000-8000 Chinese characters. What word count should I be aiming for when I write the English version?

The text is about mathematics, but since it is an overview intended for a general scientific audience it will not be overly technical. In particular, it will contain some  mathematics terminology, but almost no mathematical equations.
If you plug the text you just wrote into Google Translate, then paste the output of that into wordcounter.net, you get 151 characters from your above 96 words.  That approximately matches my experience.  Plan for about 1.5 characters per English word.