As a German lerner I can tell you that how quickly you will get your first students will pretty much depend on your prices and availability. Writing interesting discussions about learning German and articles may help somewhat. How to keep those tudents is hard to tell, because I guess everyone likes different things. Also, I still have to see a German teacher who managed to teach English here and have students. Competition is hard and everyone prefers a native speaker. But don't worry about that, German is much better to teach.

As for how much work they put in, not much. You should, as a minimum, have some conversation topics ready and be able to keep the conversation going. Other than that, you don't have to prepare at all, but you may have some advantage over others if you do.