There are the obvious worries about getting scooped (discussed here http://www.quora.com/When-is-it-wise-to-blog-or-talk-about-your-academic-research-work-before-you-submit-it-for-publication).
But I'm wondering if there are more subtle concerns. Could it hurt your chances of publishing in a venue that doesn't allow preprints? Should I cite myself if I copy text?
I remember very clearly when an editor for Science was asked about whether or not they would publish work if it appeared in a blog post, the editor replied with "so long as it has no more than 70 likes, 20 share, or 30 re-tweets". She was actually being satirical, and ended up having to restate that Science doesnt care so long as "the core scientific message" is novel in their publication.
Truth is, I hear a lot of stuff like this from journals claiming to be all about the dissemination of science. What i DONT hear is people who's work was rejected specifically because of a blog post. Probably because the rejection letter is the same old standard "Better luck next time." and the real reason is never known.
Long story short, if you want to keep publishers happy, do whatever you can to make the article valuable...
About your first question you should consult with the conference or journal about putting your content on preprint servers (e.g. Arxiv), the policy of different publishers might vary.
About your second question You should cite every content you copy, even the content you copy from your previous research and papers otherwise it would be a case plagiarism or self-plagiarism (copying your own content without citing properly).
