I am creating article blog and think a lot about SEO. The question is how should and what headers should I send.

If the article is changed, okey, I am changing Last-Modified header. But what if there are new comments to article, should I change header? Or search engines will not scan my web page again due to old Last-Modified header?

Also, is it okey to use both Last-Modified and ETag and Expires or choose one?