If by "first class buffs" you mean get the IM buffs after maxing the first class buffs, then resetting to mage, it can't be done. A muse can only get two of the IM buffs (Advanced Hustle Char and Advanced Resilience Charm) before job change to cleric. After that, you have to max the cleric buffs to get the rest of the IM buffs.
No i mean, you have to get the first and second class buffs for cleric, then after you obtain the IM skills, you'd reset to using the more attack based and basic skills. You could even have small AoE's from first offensive class skills. in other words its a partybuff/offensive Cleric.
I actually own these skills and I know the req's for them, and am currently working on building one. So far in one day i got to lv52 and in about 4 days ill have this hybrid.
Edited by Feuer, 09 September 2010 - 01:32 PM.