*You want enough vegetables that will fit onto your sheet pan in one layer. 8-9 cups fits onto a half-sheet pan. The key with roasting a mix of vegetables is to make sure the cook time of all the vegetables is as close to the same as possible. Factors that affect cook time are size of the pieces and density of the vegetables.
The only vegetable I don’t recommend using for the roasted vegetables are carrots because they are in the romesco.