3. I have worked in shops in which designers threw Photoshop files, JPGs, or something similar over the wall to developers. Because of the differences in emphases and priorities between interaction designers and developers, the results were generally disastrous. Of course, this is the extreme end of the spectrum, but hopefully, you get the point.
4. All that said, I strongly recommend the interaction designer create the HTML and CSS. I know for some IxDs, this might smell and taste like coding, but in my experience, without the IxD doing so, the user loses -- in some cases, a lot -- and that's what we're here for: to advocate for the user.
5. Some tools might create a good start to HTML and CSS, but I would never leave to the tool to do so. I'd always check its work.
7. My bottom line is this: If you have it in you, and it's practical in your organization, create as much as you can for the user, because it's in your best interests, and yours are the user's interests. I like dom.latham's suggestion of partnering with developers if this is not possible or practical.
Am I understanding you right that you mean it's better for interaction designers (and maybe ux designers) to have a technical background, or at least deep technical knowledge about how his/her interaction patters are implemented in code?
You don't fear that this can hurt the design, in the way that the you know too much about the implementation model? Me, I started in the engineering department and I often wonder if my deep knowledge about technical stuff will stop me from becoming a great interaction and ux designer. If it will stop me from thinking outside of the box.