I'd ask, "safe from what"? Chickens must be protected from canine predators for their entire life time; coyotes and feral dogs can be exceptionally hard on chickens even when they're adults.
Three week old chicks are still dependent on external heat sources, either a brood hen or a heat lamp. I turned off my heat lamp for good when mine were about four and a half weeks old, but they're still in the brooder at age six and a half weeks, I won't put them in the run/coop until they're eight weeks. I don't have any other chickens, so none of the cockerels can defend the rest of them. They can't defend themselves yet, though I did have a real face off today between two cockerels, hackles raised and everything. One of them blinked so there was no actual fight. I think they're establishing their pecking order now.
You are passed the "pasty butt" stage, soon to be passed the heat lamp stage, then it's feed and fresh water as needed until they can go into a coop at 8 to 10 weeks (sooner if the weather is warm). Then they're in the coop (three to four sq. ft. per bird) and a largish chicken run full of grass and weeds for them to dig. I'll be putting down some scrap plywood on the ground, that will encourage bugs and worms to gather, they'll have a feast.
