https://www.youtube.com/watch?v=a_3_tjWcZVg
Never tried it, but it's on my list.
Add grated onion, garlic, powdered cumin, powdered coriander, paprika etc.
Loads of recipes on the web
Don't and buy it ready prepared. When you cook at home, it should be better than a restaurant. If it's the same, then you may as well go to a kabab shop and get it there.
"Kuyruk yagi", i.e. tail fat of sheep is usually not available in Switzerland (or most of Europe). There are nevertheless some places that do decent Doner in Zurich such as Demet Metzgerei in Zurich. One of the options is using something similiar to ghee or Bratbutter sold around.
I know I am not exactly answering your question but just in case you're also interested There's no single way of making doner as the choice of meat will depend on chef's and eater's taste but usually it is made of the highest quality meats and hence is not a cheal dish.