I have taken a stab at converting ilpizzaiolo's recipe as you have adapted it to include use of a starter. Using a starter complicates the conversion process for three reasons that immediately come to mind: I don't know how much your starter weighs, I don't know its leavening power, and the amounts of flour and water have to be adjusted to compensate for the flour and water in the amount of starter used. Consequently, to do the conversion, I assumed that your starter is similar to mine and is about 50% flour and 50% water. I weighed a tablespoon of my starter and it was about 0.50 oz. I then adjusted the amounts of flour and water so that, together with the other ingredients (salt, IDY, and the starter), the total dough ball weight was around 14 oz.
Since the recipe calls for the use of cake yeast and you plan to use IDY and refrigeration of the dough, I converted from cake yeast to IDY by dividing by 3, which is the typical conversion number used. So, 0.75% cake yeast in the recipe became 0.25% IDY (by weight of flour). I did not attempt to reduce the amount of water in the recipe to compensate for the liquid in cake yeast. I suspect it is minimal in any event. Since your starter has leavening power, you may be able to reduce the amount of IDY somewhat, but I have no way to tell you by how much.
I realize that you are planning to make two pizzas, each using a dough ball of around 14 oz., but I have listed the ingredients and quantities below for a single dough ball, along with volume measurements for those who do not have scales or want to make just a single pizza. To make more dough balls, all that is necessary is to multiply the weights (or volumes) by the number of dough balls desired.
You may also be interested in knowing that the thickness factor (TF) for your pizza is on the low side. I know that you favor your pizza crusts on the thin side (to keep carb levels down), but yours is extra thin. You indicated that you wanted a roughly 14-oz. dough ball for a 15-in. pizza. Using the expression 3.14 x 7.5 x 7.5 x TF = 14 oz., I solved for TF and got 0.0793, or roughly 0.08. A typical NY style dough has a thickness factor of around 0.10. In any event, I have presented below the list of ingredients and quantities I came up with for a single dough ball weight of 14 oz. When I added together the weights of all the ingredients, they did indeed come to 14 oz., which suggests that my math is correct. For those who may want to use the original recipe, i.e., without the use of a starter but using IDY and refrigeration, I will do another conversion and post the results in another posting sometime today. I welcome anyone to double check my figures (and methodology) if they are so inclined, to be sure that I have correctly stated everything.
High-gluten flour (100%, KASL), 8.40 oz. (1 3/4 c. plus 2 1/2 T.)
Water (60%), 4.95 oz. (about 2/3 c.)
Salt (2%), 0.173 oz. (about 7/8 t.)
IDY (0.25%), 0.022 oz. (about 1/5 t.)
Starter, 0.55 oz. (about 1 T.)
As for your question about dividing dough balls sooner rather than later, I tend to favor doing the dividing sooner. This minimizes contact with the dough balls once they are formed and suitably weighed. Dividing, weighing and shaping later may force gasses out of the dough, which you usually want to avoid.