it tends to be persoanl choice on that but i find 2 chicken breasts more than enough, and as for the carbs id just eat a set amount, 150 g of cooked rice has 45 g of carbs, so work out how many carbs your wanting to eat through the day and split them between your 3 early meals
check here, i got this on a link here somewhere and im finding it really usefull
http://www.nutritiondata.com/index.html