We have our Disc Priest pop a Barrier, when the Iron Star hits and everyone but the tank currently tanking the boss, just runs in. It just makes things more safe and there's not a lot of damage going out other than that explosion.
We just use a barrier and have people pop personals when we run away for the fourth malice. If you're soaking with just one person on the fourth malice (most people do this) there will be a decent amount of AoE going on, so an AM or something during that kinda helps but isn't totally necessary.
Most peoples DPS should be that you only need to spawn one iron star, and the boss should die before the third bombardment or during/shortly after. You really don't want to spawn another iron star because it's pretty annoying to deal with.
The last phase is solely about people not falling asleep during malice, not spawning more than the first iron star (ideally) and having that first iron star hit Garrosh at the right time. Spawning 1-3 adds isn't the end of the world, but anymore might cause problems.
One important thing is for the 3 players to spread out immediately after spawning the first iron star, or else you might spawn another iron star and that would be a lot more difficult to deal with.
Also when the iron star hits, you will become spell locked.