Limit characters when wirting a post

This is kind of a tricky question

I don’t mind editing core files (edit-form-advanced.php), I just need to know if there is a way to use something like the Maxlength Plugin (http://remysharp.com/2008/06/30/maxlength-plugin/) to limit the quantity of characters on a wordpress post when writing it

i couldn’t find a way to do this, i know i can limit characters once it is published, but i want to limit them when writing the post

if there is no way to achieve this, it also could be useful a way to count the characters i’m actually writing

thank you!