I was was raised on a 5 acre pig farm, in the Rainier/St. Helens area of Oregon. I still grunt when my wife scratches my back and hits just the right spot... LoL. It was our primary income, until the early '70s. About a third of the property was pasture, and the rest was woods and brush. There were some evergreens, but most were maples and alders (i.e. deciduous trees). The pigs did require some additional feed (especially in winter), but got their main food from the underbrush and grasses. We kept a lot of pigs on that 5 acres. Usually between 100 and 300 head, if you count all of the piglets, weaned pigs, brood sows, butcher hogs etc. Our herd cleared brush better than anything I've seen before or since. If you only want a few they should do fine on that acreage. You might want to give them additional grain "treats" so they stay tame and will come to you. Make sure you have a good electric fence perimeter, and good shelter for them. We divided the property into smaller runs so we could control where and how much they foraged. You'll want to keep at least 2-3 or else they get bored and lonely and will try to roam to find friends and entertainment.
Hope this helps!