Fran couldn't answer your questions as to number of tomatoes except to use your own judgement because she doesn't generally use beefsteaks.
No onions go into "real" Marinara. Having said that, I personally like onions in sauce. By the way, depending upon from which Italian community a person hails, often determines whether they call many forms of tomato sauce "sauce" or "gravy."
By the way, she also makes a "New York" style cheesecake that puts even the famous cheesecake makers in Manhattan to shame. Or at least according to many from both New York and Tennessee who frequently go to New York and who define Cheesecake as their all time favorite dessert. The darned thing even weighs more than any cheesecake I've ever lifted of even greater size. People have been telling her for years she should sell it to very upscale restaurants. She won't of course and sorry but she won't give out her recipe to even her best friend.....and that is the only recipe she has that she won't share.
And finally think about this.....a chocalate tort made from crushed saltine crackers, eggs, sugar, vanilla, chopped walnuts and a cup and a half of bourbon and which is topped with a merengue. All I'll say is it is out of this world and in case you think that all the alcohol is cooked out, I'll only say don't have a large slice and then drive. That was my mother's dessert and I wish I could find the recipe as it's also my favorite. We have it somewhere.