Google is penalizing sites with less content and according to some, adding more articles makes your site content rich. Can I add article on any theme on my health related site in order to just make google think that my site is content rich.
No. The content has to be specific to your niche. Irrelevant content will have no value in terms of SEO. What you seem to not understand is that pages get ranked, not sites. So even if your article ranks well, it will have no effect on your site as a whole.
Perhaps you could map out a plan of ten related topics on the same overall theme of the site. Each topic should be an individual page, with specific keywords identified. Titles and keywords should be unique to a page, and not several pages with the same content. An SEO designed site and backlinks must be supported with good seo content.
You can add as much content as you can. It is always good but make sure you have quality content along with good keyword density in it.
Keyword density is actually one of the factors Google Penguin is aiming at. Over optimized content will immediately send red flags to the system and your page could get devalued as a result. You should focus on good quality content instead. Your content has to be readable and actually make sense for it to be deemed valuable by search engines nowadays. Your content should flow naturally and you should avoid any great hat tactics such as using variations of the same word, misspellings or alternating between singular and plural forms of the same word.
Your content should not be optimized particularly, if you write on a specific subject then it will naturally contain the keywords you want to rank for. Aim your content to humans and then you will get more google pluses and Facebook likes, that sort of social media is what Google wants to see.
It is basically all about the quality content and keyword stuffing. Duplicate content and keyword stuffing is strongly disapproved by Google and sites get penalized for that.
Yes I think you must have to update your website its a good/healthy activity and Google will definitely count it.