On each Wordpress site I have worked on, the Portfolio tends to be image-based and is used to showcase work or products. Unless you have a need to do this, the portfolio tends not to get used that much. That said, I am sure there are lots of people who do use it - I haven't or really seen many sites use it.
To answer your questions:
- What are the benefits of a portfolio page over Static Pages & Posts
See above. Pages are your main structural pages.
- When creating feature rich articles should i use static pages, posts or portfolio.
Articles should be sat in the blog section, which is populated through 'posts'.
I hope this helps.
-Andy