In the process of doing the same thing. Has anyway used the German-Australia working holiday visa (12 month stay)?
It's hard to find information on, especially the German health insurance and what it will cost etc
It's 12 months.
You can use normal travel insurance until you get over there then hopefully once you find employment your employer will pay your mandatory health insurance (you also pay a portion but it comes out of your pay automatically).
Having said that I didn't really work for the duration of my working hol visa (only a few cash in hand bar shifts) and got proper insurance once I applied for my new proper visa.