Mill the juice until only seeds and skin are left in the strainer. Pour juice into large sauce pot, already on your range. Turn on the burner and repeat with more tomatoes. When you have done all the fruit, clean-up and prepare the remaining ingredients. You want to cook down the sauce so it will thicken.
Taste is individual.
We like onions and garlic, so I chop and add them to the pot. The amounts are a matter of strength and choice. Same with roasted red peppers. Use your judgment with quantities, but remember that pizza suace should be peppery. I use a third of a cup of virgin olive oil per quart - measured at the time I add it.