I brew 5gal batches. I do a two batch sparge, one 60 min soak with enough water to cover my grains by a few inches keeping my Temps proper for what body I'm going for, and stir it gently for a min and let it set and check at 30 min temp and stir. Then I drain it and do a rinse with the remaining water ft hat will make up. My post sparge pre boil amounts. Yes calculate each batch. I calculate my water amounts based on grain absorption and boil off. My water batch for my most recent rye ale, was 14 lb grain bill, 8oz of hops, with a 5 gal finish is about 7.5 gal pre mash, no water added after sparge. But a good wart chiller is recommended for that technique, a slow cooling time can lead to off flavors.