Very nice Tumba. I like the style you are going for.
Not many German lookers in my neighbourhood, and the interpretation is more simple. I see a few with VW relatives wheels on as a start. Vanagon or VW busses, Audi TT rims on one.
I think 'function dictates the form' is the right idea. Modern twist to the old shape. I love the watercooled engine, although I run an aircooled myself. But i like the Subaru solution, even a rotary will be fine
