[DiapDealer]

We're not sopeaking from personal perference. We're speaking from experience. The title tags are required. Even if they're empty. An external stylesheet is highly recommended (but not required). If there's a stylesheet in your epub that's never linked to an xhtml file (in the head), most validators and/or epub checking tools are going to warn you about unused resources.

To learn, take out what you think you should be able to, and use EpubCheck to determine if you were wrong. There's no reason for you to blindly trust our opinions on the matter. Use EpubCheck That's what it's for.