inomcoke, there is no 100% accurate answer because no one REALLY knows how google decides duplicate content or not, everyone can say this and that but NO ONE can ever give any proof. As one previous poster said, news sites often have the same news and there are many many news sites that rank highly with good SERPs and great PR etc like cnn.com news.com ninemsn etc etc. Having said that I'm sure google have some way of penalizing duplicate content on junk article sites across the web as they did announce an algorithm change a week or so ago
There is no problem in submitting one article to different article submission sites but it is better to write two article an then submitting it to different submission sites can be better. But mainly people submit one article in different article submission sites and sometime they spun the articles before submitting.
Yes you can do this and it has no limit, but you will not see much of an impact on your work. Google can see duplicate contents and if it does from what i know you will have very minimal value for the link. It is always better you have unique content and to make things easier try manually creating spyntax articles and generate unique contents. You will only need an extra half an hour from writing an article.