I use the three finger rule to select breeder hens because the wider the pelvis bones the bigger the egg she lays and my costomers like larger eggs. I've also noticed the chicks are healthier hatching from larger eggs , as they have more room to grow. I think that rule applies to production as...
Yes it's fine to manually turn the eggs I open my incubator to turn them it's really more natural when a hen turns them she gets up to do it so why can't I. And yes I would drill a hole before the eggs cook and won't hatch if it gets to low cover up half the hole with tape or a coin is better.