Is there such a thing as unhackable, no way in, forget about it?
Yes. If a computer is a) turned off b) disconnected from the network(assuming remote attack) c) Has absolutely no services running.
Realistically, any server that has real services is going to be hackable. This is really more of a philosophy question though.
I would be little help with your other questions so I'll let someone more knowledgeable help you.