I've stopped at every *9 tier for PvPing on my own Priest. It's a bit of a ritual I have on my characters, to learn my class in PvP one tier at a time so the learning curve isn't too humongous at 70. (Or 80, soon enough) At 29, you are going to have your **** handed to you if you don't get a bit of gear together. Half the opponents you meet are so God-Mode cheats - twinked out of their ***** that you will die if they sneeze on ya.
So yes, your gear really does matter. Use Atlasloot or whatever to take a look at the various instances available to you, and what loot is in there. Don't focus on Int/Spi too much. You need mana to heal/damage, but you won't be doing either if you aren't loaded up on Stamina. Personally, I always go for the BG gear as well. Boots and Belt from AB. Cloak, Ring and Trinket from WSG. Then PvP trinket. Takes a while to get all of it, but in the end it's going to be worth it. It's going to load you up decently on Stamina and Armor while providing a decent bit of Int/Spi/Heal/Spelldamage.
As for Specc, on my Priest I stayed Shadow. At 29, you won't have Shadowform anyway, so you can heal anyway. If you want, you can go with a Disc/Holy build, but personally I find those builds lackluster if you don't twink like holy hell...
Lowbie Stamina enchants won't cost you much, but they will definitely help out. 100 health on chest, 7 stam on boots and so on. It's going to help you out alot.