1) Car tax calculator, as Mariusz mentioned, depends on engine type (diesel car is times more expensive than petrol car), age of the car etc:
2) Insurance calculator, it depends heavily on drivers past (age, when got licence, previously insured cars in Germany etc). It's pretty expensive first years but then gets cheaper over time:
3) Technical inspection, for newer cars every 3 years, older every second year.
4) There's no road tax currently in Germany for personal cars.
To my knowledge there's nothing else mandatory.