You shouldn't have many issues if the adds are controlled. There'll be a fair bit of raid damage from the fire spit on the stacked group it hits kind of hard, but nothing overwhelming. The tank getting nom nom'd will take a good bit of damage, but again nothing extreme. Keep an eye on the kiter, he'll take some fire spit damage and may get the single shot fire blast. I find if the kiter dies it's usally cause he's out of range and all the healers kind of figure "oh someone else in LoS will get to him."
The nice part about this fight is when Mag gets chained, there's no damage to the raid or tank and you can kind of stand around and regen mana. On my pally I melee whack at Mag at this point to get some mana back and on my Disc priest I throw out a Hymm of Hope to get the raid some mana.
You should do fine. Frankly, I think the new 5 mans are more healing intensive then some of the bosses - so if you can do the new 5 mans (and I see you have at least one piece from them) you'll do fine on Mag.
i did this fight a few days ago with my guild and i was in i333 gear the other 2 healers were well geared but even so not like so much damage goes out i couldn't handle it at my ilvl and i don't think i even went oom since u have a bit of regen during the chained phase. If i can do ok u should be fine