Hello and Welcome!!
I'm a firm believer in making sure your coop and run is protected. I live in an area with coyote, fox, owls, hawks, fisher cats (so gross!) and the wandering neighborhood dogs. I let the girls out to free range on evenings when I am home, but their roamings are always supervised.
One aspect that people tend to overlook is making sure the top of the run is protected. Some people choose to fully enclose with a roof, but I chose bird netting secured every 6" and it has worked quite well to deter overhead predator attacks (if you have trees nearby, don't forget that raccoons can climb and jump!) My sister-in-law chose chicken wire and that option works very well also.
I only have experience with a few breeds, but have heard that brahma's are generally very docile (I have one and can walk right up to her and pick her up). One thing that I am noticing though, is that all birds are different. Just as with dogs, breeds have a generalized predisposition, but their true character may be completely different. For example, cochin's are supposed to be friendly, but mine is a witch
... and in my experience, MOST chickens will let you know if predators are around. My girls are really good at yelling when they sense something out of place. My black sumatra and wyandotte are the group yellers.
Best wishes on your planning and prepping for backyard chickens!!
Diane