If using fed starter, would you subtract the port of flour and water from recipe?

You certainly can. If I were making this recipe, I don't think I would bother - I find pizza to be very forgiving and for this amount of flour I wouldn't be using much starter in the first place. You might get a slightly thicker pizza, but if you're using 20% starter to the amount of flour that comes out to 48g, which is probably a couple tablespoons. But some people prefer to be much more precise than me, so it won't hurt if you do subtract out the water and flour from your starter.