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"...duplicate content and penalize my website"
---> duplicate content is not penalized, it's often just deemed somewhat irrelevant as Google has seen the content before and has an 'older' or in some few cases, 'considerably stronger' version of the content in its Index.

..."about 301 redirection from non WWW to WWW using htaccess ..."
---> perfect solution (this is the correct thing to do), and if anything, your site will be stronger. While 301's do lose a teeny bit of link equity, any links to the non-www version of your site will now be making the www page that much stronger.

"I don’t want to lose my current rankings or organic traffic"
---> this is highly unlikely

*you may want to set your webmaster tools setting to "www "as well

All the best - Andy

I'd stay as far away from automated article submission software as I could. Do a bit of research on this topic and you will see why... just trying to help

Having the images on your site's pages is better SEO wise. The algo takes into consideration 'engagement objects' such as photos, video, etc. in a positive way. The same goes for videos. If bandwidth is an issue, I'd suggest handling it in ways that will still allow you to keep your photos on the site.

Andy

If you are trying to conserve link juice by using the no follows, it won't work. This type of thing was utilized shortly after no-follows were introduced, the practice was referred to as 'PageRank sculpting'. The search engines changed the way they dealt with no-followed links "with regard to link equity" as a result of page sculpting.

---> All followed links on a page pass link equity, and will reduce the link equity on the page the link is on.
---> All no-followed links will not pass link equity, **however they will reduce the amount of link equity on a page the same as if the no-followed link were a followed link. **

So your hypothesis, about not passing link equity to internal pages that really don't need it (contact, etc.) is a good one. However, you won't "save" the link equity on the page that has the link... followed or no-followed.

And, you are also correct in deciding to not use the no-followed links in this manner. I wouldn't bother using no-follow links for the purposes you've described. As for navigational linking, I wouldn't worry to much about link equity, as the search engines are getting better and better at determining the importance, or lack thereof, of links based on their location within a page. If you feel you might have too many nav links, perhaps eliminating a nav section might be a solution.

You may want to search around the term PageRank sculpting, as there may be more information provided to you this way.

Andy