That sounds like a good reason why nobody should be handing them nuclear weapons. Don't you agree?
Iran would certainly be bombed if it were to fire a nuclear missile at Israel or at any other nation. Not necessarily nuclear bombs. But the result would be that significant parts of Iran would be reduced to rubble. It would be necessary to ensure that Iran's capacity to launch any more missiles was negated, beyond doubt. Then it would be desirable to try to remove the leaders who ordered the missiles to be fired in the first place, to make sure they can't do the same thing in future.
Yes. That's another reason why it would insane, even for crazy Iranian theocrats, to start a nuclear war with Israel, or with anybody else.
Russia used to be able to track missiles headed towards its territories. I assume it still has that capability.
If they were aimed at Iran, I assume they would. Putin is smart enough and sane enough not to start a global nuclear war, I hope. He would be aware and worried about the consequences for himself, even if he was not concerned about the Russian people in general.