So, I guess you got your answer. It's between 1 - 500 word article per week and 15 - 1,500 word articles. Moral of the story: start doing, feel it out, test what works and adjust. I have a few websites that I rarely update (we're talking months) and they do just fine in the SERPs. Something more timely like sports, news, etc probably needs way more frequent updates (which is why I never go for those types of sites). It's probably best to look at what your competition is doing, and copy that first. Then, once you have your footing, test out increasing or decreasing frequency and see what your analytics tell you.