It's easy to double (or more) the recipe for larger groups. In that event, go easy on the olive oil. Depending on the type of pan you use, the amount required to sauté the carrots and bell peppers may be slightly less than the multiple used for the other ingredients.
I find that the balsamic glaze is tasty enough without salt or pepper. Of course, if you decide they add to the dish, by all means add them at the end, after you've tasted glazed vegetables.