All of your articles have to be unique (at least 50%), or else your article marketing campaign will be a big waste of time. If they aren't unique, the search engines will deem them duplicate content and they'll be removed from the index.
The duplicate content stuff is just a myth. I always submit the same exact article to multiple directories, and have never had a problem. The only suggestion I would make is that you might want to change the anchor text for the links in your resource box (use a different anchor text for every few directories) to get the MOST out of your backlinking efforts.
Your going to get 2 different answers here. YES and NO... You don't get penalized for duplicate content. plain and simple. Here, check this out - I write and article, put it on my site, then submit it to ezine articles, (without changing anything) link back to my site, then submit that same article to thousands of other directories, and link back to the ezine article and to my website. I get an insane amount of traffic this way and I fluctuate from page 1 and page 2, for my keywords right now. I'm sure I will be on page 1 here shortly.