At one extreme you have a site with thousands of fee paying students and where a failure could nearly wreck your school. That requires a Moodle Partner level of skill and commitment,
For a single class MoodleCloud is the best option. It can get more expensive if you have several hundred students but installing Moodle ALWAYS costs - in money or time.
In between these, I suggest installing yourself. You have Ubuntu and updating and installing a LAMP stack is well documented. From there follow the Ubuntu step by step guide. Any questions post here.
Most problems people have here is because they try to install on a home computer running Windows or a Mac. Sticking to a clean Linux server as you have done eliminates many problems.