Already said more or less but priority is making sure enochian has 100% up time, being able to cast another FireIV only for enochian to fall off and having to wait for cd's would be a significant dps loss.
It takes practice on timing, but really is second nature once you got it down.
Black Mage is fine as is i think, yes it was a change @ 60 but was honestly for the best as some found 2.X blm too boring. Those that truly love blm will stick with it, it may not be for everyone.

Also do not use leylines, all the mechanics are based on blm using leylines
(P.s i am joking about not using it)