Black Mage isn't at all hard. The rotation is simple throughout its entirety as others have said. Though I've heard here and there that the AoE rotation still a foreign concept to some level 80's out there.

Movement becomes less and less of an issue once you learn to look at Swiftcast and later Triplecast as not only burst/frontloading options, but as movement options. Our HP pool is the same as all other DPS Casters and is dependent on gear.

Also, if you REALLY don't want to move for a moment, and you know a certain AoE isn't going to do something wacky like debuff or outright kill you... Pull a "Healers Adjust" move and use Manaward. Out of all the DPS Casters, as far as I remember, we're the only ones with a self-shield to mitigate damage.