There is a big difference between “information” and “instruction.” They did a good job providing information but terrible on instructions. Therefore it really isn’t for newbies as promoted. As a certified tutor I learned and practiced strategies like “peer to peer” mentoring, intellectual scaffolding and tackled the Zone of Proximal Development” for foreign or special needs students on a college level.
The topic you choose must have enough depth that you can create a lot of content for it. This is important for building an authoritative site, for search engine optimization, and most importantly, for the end user. If you don't have enough content about a topic, you're not going to be taken very seriously as an authority on the topic and it's unlikely you can convince someone to make a purchase from you.