I have an LGD, a Leonberger, to protect the chickens & the alpacas; but I think our alpacas could take care of themselves against our biggest predators, coyotes. They do seem to act as a group to chase our 100 pound dog out of the corral. That being said, they're certainly not regarded as a herd...
Their primary diet should be a good quality orchard or grass hay. We give 1/2 a cup of alfalfa pellets to our pregnant females & also use handfuls to socialize our herd & also free choice minerals.
The alpacas will probably leave the mineral block alone. Mine don't touch the horses mineral block, although they could reach it if they want to. I'd really recommend the Stillwater Minerals for your alpacas. Our breeder recommended it & we always have it available free choice for our females.