According to Evelyne Slomon, who wrote the book The Pizza Book
and who knew and worked with the old masters who made NY style pizzas with their coal ovens, the pizzas varied in crust thickness from one pizza operator to the other. However, I believe that the amount of dough that Terry Deane is using, 22 ounces, or about 624 grams, is a good value to use. It corresponds to a thickness factor of 0.0865. I think anything below 0.07 gets to be too thin. However, it is your dough, so you should feel free to experiment for yourself to find a value that works best for you in your particular oven.
As far as the crossover point for using oil in the dough is concerned, I would say that it is the temperature of a gas deck oven. According to Ron Molinaro (ilpizzaiolo), oil (and sugar, as well) was added to a NY style dough when gas deck ovens came into being, as he noted at Reply 3 at http://www.pizzamaking.com/forum/index.php/topic,1053.msg9384/topicseen.html#msg9384
. Today, most gas deck ovens have a maximum operating temperature of around 650 degrees F (see, for example, http://www.bakerspride.com/specs/superdeck/SDECK_D125_D250.pdf
) but most operators don't use temperatures that high, although I understand that Dom DeMarco has an old Bakers Pride gas deck oven that appears to be an exception. If you will be operating at temperatures above 650 degrees F, you don't need to add oil although that is something that you might also want to experiment with.
As for your peel, you might at least smooth the surface with sandpaper. Like Terry, I also have a 20" x 21" wood peel and it nicely handles an 18" pizza. However, if you examine your 18" peel, you will see that the sides are tapered. In order to get a full 18" pizza skin on that peel, the skin will overlap the tapered part of the peel. You will have to test whether that impedes loading an 18" pizza into the oven. It might be close.
Please keep us posted on your progress on this project.