A 1 lb box makes 8 average portions, assuming you will have something else too. Since a box of pasta is cheap extra is not much of a problem, but a half box (8 oz) should be fine, no more than 3/4 of a lb max, good luck.
3/4 of a packet, 1 if you want leftovers. For something different, add tuna to the sauce, it's really yummy. Use 1 bottle of passata and 1 can. Fry some chopped onion and garlic, add the sauce and the can and cook it on a low simmer, add salt and fresh/dried herbs like parsley. Keep an eye on it, add a little water if it's too thick. Good luck.