What's the minimum number of keywords you can use in the homepage of a website? I've seen a site that has a lot of keywords but rank better in SERP.
All you need to do is to make sure that your title clearly communicates the subject of your article and then just make sure you write a nice article that is uniqely yours. It is better to have every page concentrate on one subject only so that search engine can interpret your page easier.
Matt Cutts explained keyword density really well in this video here
Keyword stuffing is considered to be an unethical search engine optimization (SEO) technique. Keyword stuffing occurs when a web page is loaded with keywords in the meta tags or in content. The repetition of words in meta tags may explain why many search engines no longer use these tags.
Keyword stuffing had been used in the past to obtain maximum search engine ranking and visibility for particular phrases. This method is completely outdated and adds no value to rankings today. In particular, Google no longer gives good rankings to pages employing this technique.