I don't agree with the handling part re roosters. I would say it actually varies heavily based on their breed and individual disposition. I dont have any tolerance for aggressive or overly skittish flighty birds. One bad one spoils the bunch. If you're more cutthroat with your flock member...
Deathlayers are an extremely delicate breed for awareness. They're similar to Sebrights and Polish that their immune systems are not as robust (i.e. Mareks would wipe out 100% of a Deathlayer flock). It's a shame, they're a beautiful breed.
Cornish are actually hard to sex, it's easy to rehome a female for young ones with slightly pink combs. If you can, wait another month and repost before selling if you can't keep males.
The Welsummers are easy, any with red breasts and gold on the back of their necks are females. Welsummer roosters will have a black breast and tail. I see 2 males above total so far.