[Jellby]

-I want it to start the first letter of the first paragraph in a chapter with a huge bold letter (http://epubzengarden.com/?style=mode.../chapter1.html) like this.

span.drop {
  font-weight: bold;
  font-size: 300%;
}

and in the HTML:

<p><span class="drop">T</span>his is the first paragraph of the chapter.</p>

-I want it to not indent only the first paragraph and indent all the rest for easier reading.

h1 + p, h2 + p, h3 + p, h4 + p, h5 + p, h6 + p {
  text-indent: 0;
}

and make sure the chapter headings are indeed marked with <h1> to <h6>

-I want it to have some kind of code for italic part and that the margin is set to lets say 1/4 of the page width or something that looks esthetic.

Use <i> for italic.

For the margin:

@page {
  margin: 25%;
}

but I'm sure that's not what you want.