How much weight depends on how large the goat is and how good of shape he is in. My two larger goats are about 200 lbs. The general rule for an average goat is 1/4 of their body weight, but I wouldn't hesitate to put 1/3 of their weight on them for a shorter trip.
If you are hiking in and out of the back country, you will want to go lighter. Having the goats in shape helps. Mine were pasture potatoes this summer, so I had them carry the quarters and I carried everything else boned out.
They are low maintenance and, as the pics show, I didn't have any of them on a lead. I get out of the truck, let them out and walk. They'll stay with me all day. You can trim the hooves with a fine pair of trimming shears from the home and garden department.