Goats are not hard to deal with especially in comparison to tradition pack animals (ie. horses, mules). They are small enough that one can "control" them. They don't take any special training and the first time you strap a saddle to them they seem to take to it like a duck to water. I'll load anywhere from 20 to 40 lbs. per goat depending on the terrain I'll be hiking, but I've read where they will haul about 30% of their body weight.
I don't haul feed or water for the goats. They browse on whatever is available and I may carry them a snack or two. When out hiking a goat's body will shift into a "desert" mode and they will actually recycle their urine. I've never been out more than one night at a time so far, but have yet to have a goat take a drink when on a hike even when I tried to water them. I've read where they can go up to 3 days without drinking depending on the moisture content of their feed.
Most of my equipment is homemade. I was given one saddle and two sets of paniers. From that a friend of mine built 9 saddles with panier sets for all of them. A typical euipment setup will run about $200 per goat.
As far as what kind of goat, just about any goat will pack including the pygmies. Of course you will want a big strong goat for packing. I have 5 goats and 3 are good packers the other 2 are really pets, they didn't cut it, although they will pack they tend to tire easily. Of the three good ones, two are LaMancha crosses and one of those is a LaMancha/Sannen cross (the white one). The brown and white one is probably the best packer as far as strength, stamina and overall muscle conformation. He is a Boer crossed with some Spanish mixture. He's a really strong good looking goat but has an anoying bleat. I will be looking for some more of the Boer crosses for my next generation of packers.
You can start packing a goat light at about a year and half or so, but they really come into their own at about three years. They are very similar to deer in that they hit their prime at 5 to 7 years. Nuetered billies are the prefered sex. My 3 goats are 3 1/2, 4 and 6 years old.
As we start to age it seems the packs get a little heavier and the trails a little longer and steeper. The goats are certainly a welcome addition to my "hunting gear" and a lot less weight on my back makes for a more enjoyable outing which after all is the real reason we spend time in the outdoors to begin with.
Scott