Because there is a lot of pasta and vegetables in this dish, one medium to large chicken thigh per person is sufficient. You don’t need extra oil for the onion and garlic because you have the juices from the chicken and they don’t require much oil to cook.
I normally use macaroni or pasta twists for this recipe, but spaghetti chopped into thirds will also work. For stock I find 350ml is a good amount. But its all about the stock covering the contents of the dish, so if you have added extra pasta or extra vegetables you will need to adjust accordingly. We also use this chicken broth as we find it is better in flavour and quality.