[navi tasan]

Which of these is correct.
1-They had several cooks in the restaurant. They had a cook for cooking the main courses and a cook for preparing the deserts.
2-They had several cooks in the restaurant. They had a cook to cook the main courses and a cook to prepare the deserts.

3-I was their cook for preparing salads.
4-I was their cook to prepare salads.

5-This is our oven for cooking cakes.
6-This is our oven to cook cakes.
7-This is our oven to cook cakes in.

(I know the question might seem a bit weird, but in my mind there is a logic to it. I also know that I ask this kind of question often. I have a problem with this postmodification thing.)