How many articles do I have to write to generate a sale and to how many article submission sites should I submit my article to? So far I'm submitting my articles to 3-4 article submission websites.
There are so many factors it really doesn't boil down to how many articles. Some articles are going to receive a lot more traffic than others. Some will convert better than others. Just focus on providing quality content, everything else will fall into place hopefully if you are receiving targetted traffic.
I heard somewhere that you should focus on creating at least 50 pages of solid content on your site before monetizing or even trying to get traffic. Any less and visitors are not convinced that you know what you're talking about and don't feel motivated to return. As for article submission, submit to as many sites as possible. The more sites you submit to, the more awareness you create for your site, and the more traffic you generate.
It depends on your persistence, and experimentation of various methods. There's no magic number. You get out of it what you put in.
Article submissions is only effective if your web page is talking about values and such, it really depends on your niche. If I were to own a video game web page, article writing would be no good, but if my web page was about cancer, that would be another story.
Articles work towards your overall credibility and reputation, and the benefits are mostly medium to long term. I don't think you'll have overnight results with it.