Libertarians aren't anarchists. They don't generally believe that there should be no government (although you can find people who believe just about anything). I don't think there's anything hypocritical about libertarians taking government contracts for defense. If they were taking government contracts or jobs around regulating markets or building public housing, then that would be closer to hypocritical, but I'm not sure that even qualifies. Hypocrisy isn't benefiting from something you disapprove of, it's engaging in it, so arguably, they'd have to be the ones issuing the laws they disapprove of for it to be hypocrisy.
Maybe, but not necessarily. It really depends on what they actually believe (or say they believe) specifically. If their belief is "societies work better when governments don't interfere with markets", then their beliefs say nothing about what individual people should do in situations where a government does interfere with markets. They may also believe that if you can't fix something, taking advantage of it is justified, in which case they are not being hypocritical. That's not to say you can't regard such a position as unethical. However, I think many if not most people use systems they are in favor of dismantling. For example, people who believe housing is a human right don't typically donate their houses when they move, they sell them on the open market.
