I was an early employee of Quora and can vouch for it being a good place to do content marketing! I really love that site.

The idea that you should have a small scope and narrow focus is the one very common piece of startup advice I struggle with. In my experience at Winnie, whenever we "thought small" growth would stall out. I think if your product is just better with higher numbers of users, get as many people into it as you can.