Nutrition strategy

Hello everyone! As training is ramping up and the sessions have gotten longer the race has started to get very real(70.3). Question for you guys is what is the best setup for nutrition on the bike? I have a regular road bike. Nothing fancy. I have two bottle holders right now in the frame. What is the best setup? Bigger bottles one for carbs and one water? How much can I rely on the on course for my nutrition? Was planning on using a 700 bottle filled with maybe 140-160g carbs one with just water with electrolytes and some gels. Any better suggestions? Do I need a third bottle?