I'll try to answer your questions.
Broodiness is influenced by a chicken's hormones, so there is no way to tell when or if a chicken will go broody until the bird does so. But there are some breeds more prone to go broody than others, Buff orps and RIRs are two of them and I think the other chickens you listed are as well.
A good mother hen will throw herself between danger and her offspring. My neighbor has 2 cats that visit my yard often and I have 1 cat. My hens usually hatch at least 1 clutch of eggs a year and I have never lost chicks to a cat with a scary mother hen protecting them. Broody hens are usually pretty good at defending their chicks from small predators, sometimes even giving their own life to protect the chicks.
will my elder rooster and other hens bully the baby to death
[FONT=Verdana, Arial, Helvetica, sans-serif]This depends on a few things. Are the birds allowed to free range, what size enclosure are they in, how many hiding places are there, is the broody low on the pecking order?
In my experience, older roosters do not bother broody hens or their chicks. Young roosters may try to and get put in their place by angry mothers. Depending on where the broody sits in the pecking order, the other hens may stay clear of her, or still pick on her and her chicks a little. Free range broodies usually keep distance between them and other members of the flock, especially on the first few days after hatching. If in a run or enclosed area, provide plenty of hiding places for your broody and her chicks and it is usually recommended to separate the broody from the run until the chicks are older and have their feathers grown in.[/FONT]
[FONT=Verdana, Arial, Helvetica, sans-serif]As to what hens to let hatch eggs, that is up to you. If it were me, I wouldn't let the broody hen sit on any eggs until she has been on the same nest for at least 3 nights. If she stays on this long, she will likely stay on the eggs until they hatch.[/FONT]
