It's better to have few pages which are optimized than many pages wich are not optimized !
Honestly, a website (even a static one) of 5-6 pages may already be competitive. It can offer a good compromise between investment and benefits.
Clearly, it depends on your target, your sector, ... Check out the sites that arrive first on Google with your preffered keywords and you'll get a profile of how big your site must be to get into the competition !

