A standard sized donkey can carry around 200 lb. A good load for a mini is 80-100. You can ride a standard, but with their small size comfort might be lacking, especially in the hills. I feel much more comfortable on a big horse. I don't recommend riding very far in a pack saddle either. Your crotch will suffer badly even if you add stirrups. A riding saddle for a donkey might be a little hard to find.
