They have people drive them to Costco and the court. They take buses and it is not uncommon in an Amish Community for one of them to have a phone line in a barn for emergencies.I have seen them use farm equipment that they technically shouldn't use and plenty of them just farm out the labor to someone who will use the equipment. They usually have "go to" people outside of the Amish sect that does shit for them that technically goes against their beliefs.
I have lived around Amish people my entire life. I am in a county that is famous for them. They are in no way self reliant. They are a cult that at this point, only half asses their own ideology.
You have a big misconception about Amish. They are not minimalists in any sense of the word. Don't let the button thing fool you. They're just a shitty cult at this point.
And the Amish definitely pay taxes, even for schools which they don't use. (An exception is social security in the US because they were exempted from the very start, but they can't collect it either.)
Also, how is having horses pull buggies cruelty to animals? Horses are working animals, and it's no great hardship for them to pull a buggy or a plough. They can be overworked or treated roughly, but so can any animal.
In my own little vision for a self reliant future i see room for lots of stuff...buildings, equipment, many tools, small ag, etc. Definitely in line with your comment.