You can use whole tomatoes if you like. Just put them under hot water for about 10 minutes, until the skin is soft and can be easily removed. I used a green onion, because I happened to have it on hand, but if I didn't I would have used about 1/4 cup of sliced yellow or red onions. I'm a fan of using what you have! For the spices, I used a few dashes of the basil and oregano. Hard to quantify, but if you are unsure just add a little at a time tasting in between. I also added a dash of red pepper flakes for some spice, but you can leave that out.
As with any pasta sauce, adding veggies or ground meat can be added. I have found on many occasions this pasta sauce really doesn't need much. The tomatoes give it a nice hearty taste, without being too heavy.