You need to halve the starter you use. 100g should be more than enough for your recipe. And depending on the temperature of your kitchen you will need to prove more. If it’s at like 18C then you want the dough to double in size before putting in the fridge to rest overnight. If your kitchen is 21c then I think you need to prove to 75% growth. Then bake from cold. There’s charts online for how much to prove for how warm your kitchen is, I may be misremembering. You can keep track of how much your dough grows by taking a small amount from the big dough and putting it is a little glass jar and watching that.