Not only is it frustrating but also painful to edit a chapter for thirty minutes or more then make a big mistake (eg. Pasting the same chapter in the edited one or mistakenly clearing a paragraph) and having no way to undo it.
I have made this same mistake twice and I had to edit and edit for...
The first chapter of a fiction is very important.
Readers should be able to get an overview of what the book is about from it, if you drag it out or write too much at once, that might kill the mood you are trying to portray.
9k words doesn't give a break for someone who just started reading...