Kendra, Keep in mind I consider myself a pig failure...
1) yes when they are too small to defend themselves, but mama should protect them at that age, once they are fully weened there are few predators that present an issue.
2) Mine didn't bother with the chickens or ducks. Didn't even mind the chickens standing on them. When the chickens would get into their food, they would goose them with their snout.
3) Yes, but you have to train them early to the wire. AND you have to have at least a 2 joule energizer, bigger is better. This is the area I failed the worst. My friend uses steal wire with a big spring to train them to the wire. The first time they get shocked they'll attack the wire, if they win, you lose.
4) if you're going to let them breed, separate the boar as soon as the sow farrows. At three months, the boar will be going after the little girls. Also have a plan on what you will do with any males that are born as they'll be frisky by about three months.
5) Fencing. Hog panels are great, but line the inside with cinder blocks, railroad ties, etc. Otherwise they'll get their nose under the fence and bend it up. Hot wire about a foot inside the fence and nose height works if they've bee properly trained and it's really hot. My friend actually just uses a single wire to keep them contained in his forest, but they get rigorous training before transitioning.