Freelance tax and Health Insurance (Stuttgart)

I am in Germany with a Work & Travel Visa. The Canadian and German governments have an agreement which allows Canadian citizens to travel here for work and vacation. As a requirement for the Visa, I have health insurance however, I'm unsure if this is enough in the eyes of the German Government. Has anyone had recent experience as a freelance teacher in Germany and had to work out the tax and insurance details (with this work/travel Visa) ? Or if anyone can recommend a professional I could speak with in regards to my situation, that would be a great help.

Thank you!