One window and one door is sufficent for kitchen with one exaust fan independently or in ventilator.
In my experience an electric chimney (60cm width) directly over the cooking hob is the best as compared to the extract fan. Earlier I used to have an extract fan & over the period the wall and the fan used to get extremely oily which is difficult to clean. An electric chimney on the contrary sucks out the oil fumes immediately and cleaning of the filter of this chimney at regular intervals helps us greatly n keeping our kitchen clean. I am very happy with the electric chimney as compared to the extract fan we used to have.