Diebold-like machines are not used very much anymore, I think because of all the controversy over how easily they can be hacked. Most of the country uses paper ballots that are counted by machine.

Yes, polls can be wrong, but I think exit polls are rarely wrong. Another comment pointed out these can be wrong too though, so this might not be a useful point.

Yes, as I mentioned in another comment, if you want to hack a real election you need to take a long-term view and make electronic voting widespread.