Could a native English speaker help me with the mistakes in this text?

I am a story writer and work for a publishing company. I've edited quite a few books so far; I've even titled some of them, sharing the writer's enthusiasm. I regarded each book to which I contributed simply a comma as if it were mine. Publishing a book is bread and butter to me. Each book has the smell of bread and butter mixed with effort at the time it is published. The one you are holding now is my first story book: I have not counted how many (insert word here) I've completed.

( Well,I am really very confused here, I am trying to say it makes me feel very relaxed and happy). (Bread and Butter)

you actually got pretty close to what you where getting at. You just need to change your verb.

(mingled-> mixed)

At the end, you end with your sentence awkwardly, you haven't counted how many what? books, stories, pages?

Excellent job, most of the kids in my english class couldn't write a paragraph, let alone in a foreign language.

I am a story writer and work for a publisher. I have edited quite a few books so far. I even titled some of them sharing the writer's enthusiasm. I regarded each book to which I contributed simply a comma as if it were mine. Publishing a book means so much to me. It makes me feel so relaxed and happy! Each book bears the smell of my hardwork and effort at the time when it is published. The one you are holding is my first story book: I have not counted how many.

I'm not quite sure what your last sentence means, but I gave it a try:

I write stories and work for a publisher. I also have edited quite a few books. I even wrote titles for some of them, sharing the writer's enthusiasm. I treated each book to which I contributed as if it were mine. Publishing a book is essential to my happiness. Each book bears the smell of hard work and great effort by the time it is published. The one you are holding is the first story book I have written myself.