That is a lot of territory to cover.
behavior around people: is highly variable. Some are very friendly with people, some are standoffish (and therefore not a liability with people) and others are very intimidating. This varies somewhat with breed, but is also a very individual matter. Nearly all are very friendly with family members, and seem to recognize children as something to protect. Buy pups from parents that have the kind of attitude you are looking for.
other dogs: most LGDs come to recognize the yard dogs and the herding dogs as a part of the farm. Some will harrass the familiar dogs in a friendly way just to keep them out of the sheep. It is fairly rare that there is a problem, and that is usually in the less common breeds (i.e. kuvasz for instance) where there is a larger propensity for dog aggression.
breeds: that is a huge topic and everyone has their favorite. It is best to learn about the breeds (look back through the archives here) and find out what the strengths and weaknesses are of each breed and then decide which one best suits your farm. If you have a favorite (such as the Pyr) then seek out breeders who produce dogs that work in circumstances similar to yours. My opinion is that you are best off purchasing pups from working parents where you can observe working style and make sure it suits you. Some of the decisions you need to make is do you need a close working dog that stays tight to the sheep, or do you want more of a patrol dog? is it important that the dog likes people? what type of predators (i.e. do you have any large predators like wolves, bears, or cougar?).
LGDs work primarily on their own. 99% of what they do is instinct enhanced by how you brought the dog up. The latter is imo quite important as there is much you can do to help assure your dog grows up to stay with the flock, and to be trustworthy. The best way to look at it is the sheep will train the dog how to behave, your job is to make sure the dog is provided the right training environment. Beyond that it is nice to have a dog that comes when called, can lead on a leash, and jump into the back of a truck should you need to move it.
I prefer to feed my dogs daily but others make use of self feeders. Feeding daily means you see the dog and the sheep every day and can check for any problems. Self feeders tend to draw rodents and birds, can lead to obesity in some dogs, or a tendency to hang out by the food rather than move with the flock. But understandably there are circumstances where feeders are convenient.
You did not ask but here is my favorite puppy rearing protocol. New 8 week old pup is placed in a pen made of 4 150 ft rolls of electrified poultry netting (because the squares are small enough pup can't escape) with 3 to 5 just weaned lambs. Pup will remain here for 2-3 months. At about 5 or 6 months old pup graduates to the dry ewe group (or ewes with lambs at side) and remains there, hopefully moving at least a half dozen times with the flock before it reaches 12 months of age. During this time I prefer electrified netting because it helps teach pup to respect fencing. By a year of age, pup should have good habits and no longer requires fencing to contain it with the flock.
Juvenile dogs can present some behavioral issues such as playful chasing, chewing, or plucking wool. this most often happens between 8 and 18 months of age during which time there are a number of tools we can use to stop the behavior. First would be to move pup to a tougher group of sheep such as adult ewes or rams, second would be to use a dangle stick, and third would be to kennel or tie pup for a few months to cool its jets. All of these tools are to buy time while pup grows out of this rambunctious stage.
As a rule pups that are 5 mo to 18 mo of age must be supervised if placed with ewes with newborn lambs. A portion of the dogs will do just fine and can remain with the lambing ewes while others need more time to mature.
consider whether you might need 2 dogs (or more). Some places have a large number of coyotes or larger predators and require more than one dog.
Tamarack Prolific and Ile de France crosses