They are an all around guard as far as alerting for sure and being "present". As to how forward and bossy in a non-livestock issue, that depends on the dog. They are vocal when something isn't right, livestock or not, and they do tend to be right up at the gate/fence, etc. During the day, if nothing is worrisome, they do sleep. They are still keeping an ear out for issues and will alert and guard, but they doze w the livestock generally and conserve energy during the day. At night is when they are busy. My male generally stayed with the herd and the female patrolled the fence. She loved to kill coyote. The male would take the herd to the barn and then help the female at the fence if needed. Otherwise he was a lazy bum and slept w the herd at night, too.
With family and known people, they were friendly. If someone was obviously supposed to be there they were generally reserved, but quiet.
They had incredible savvy on reading a situation and would guard the barn cats and anything else I brought in. Once I introduced a pet, duck, chicken, etc. that was considered "to protect" as well. I worked with a Great Pyr rescue group and both of mine were rescued working dogs.
You may be able to find an experienced working dog through rescue. If you get a pup, it's invaluable to have a good adult as an example for them. If you're starting w just pups, be sure to find a good breeder to help you, and be aware they won't be guarding and savvy for at least a year, probably 2 before they're fairly "bombproof" and truly able and confident enough to adequately stand up to serious predators.
Not all will guard chickens. Usually w some work introducing them to birds you'll have some luck. Especially if they're guarding a coop and not loose birds. A few dogs never do take to guarding chickens and may chase/kill free ranging birds.