I'm a priest (Disc/Holy) and want to start getting wow gold involved into Arena play. I own all the Season 2 gear for my class and most items that can be purchased with Honor points only. Coming next week, should i be doing Arena in my Season 2 gear or my lvl 80 Epics (Naxx/crafted/heroics epics)? Is S2 gear still viable?

The arena is one of those things where you don't really know until you try. You can math out PvE encounters to some extent, but not so much PvP. My gut says level 80 PvE epics will trump Season 2, but something like Season 4 would trump the 80 PvE gear. If you have the time, queue up for some skirmish rounds trying out different gearsets before the season starts. For a Healer, you'll pretty much want to see what lets you survive a focus fire.

Season 2 has a lot of stamina and resilience, but compare your HP in that to your HP in level 80 epics. I imagine there's a hefty difference, but does the Resilience you're missing make up for that and the load of spell power you gain? We just don't know yet. It might, or it might not. Like I said, run some skirmishes. It won't be the same as coordinated arenas, but just make a note of what kind of damage you have being thrown at you.

If you're getting 2-shot, that particular gearset isn't working. If a disorganized wow gold skirmish is tearing you apart, an organized team will kill you so hard Blizzard will delete your account and pre-emptively ban you from battle.net for Diablo III.