Disagree. Gandalf was Maia, and was therefore immortal. Being immortal didn't preclude him from being killed however, as was also true of the elves.
Melkor was a Vala (and not for long), not Valar, 'cuz there was only one Melkor.
Gandalf is one of the Istari, the five Maia selected by the Valar to sail from the Uttermost West to Middle-Earth to fight the scourge of Sauron, the second Dark Lord.
The number of the Istari was never settled on, or if it was, only lately. We can say with confidence that there were five chief Istari sent to the North-west of Middle-earth; as for lesser Istari, or chiefs in other regions, we don't really know. Tolkien did speculate that the Blue Wizards established their own magic traditions (Hereni Istarion?) in the East, which would allow us to have a great deal of lesser Istari, if we wanted them. The Istari were instructed not to fight Sauron, but rather to encourage the people of Endor to fight him. Oh, and it's not "five Maia," it's "five Maiar," cuz, well, there's five of 'em.
Gandalf is a Servant of the Secret Fire, and is not human, but immortal.
No, Gandalf was quite mortal. He died of physical injuries and his fea passed out of the world, just like any other adan. He was a durable chap, probably moreso than any Elf, but when it came down to it he received the Gift of Men.
Disagree. Gandalf was Maia, and was therefore immortal. Being immortal didn't preclude him from being killed however, as was also true of the elves.