Sourdough Bread Building Question

So I have 100 grams of starter, 100 grams of water, and 100 grams of flour on the top of my stove to ferment with every intention of baking some loaves tomorrow.  I want to make sure I'm clear on things, though, before I do anything.

I'm going with the 1-2-3 bread method.  My starter is 100% hydration.  It doubles in 12 hours.  If I make a loaf out of the preferment that I have going on with 100 grams more water and 200 grams more flour, will it work?  Should I instead think of it as a starter and add 600 grams of water and 900 grams of flour?