Okay, a couple things to note:
Saving mana is nice, but that is why we have mana gems, potions, evocation, mage armor, a shaman, and hopefully a shadowpriest in your group. With all of these things you should rarely run out of mana (at 70 raiding time).
Fire gear is not difficult to find, or more specifically it doesn't matter much if it specifically says 'increases the damage of fire spells' as it can just say 'spells and effects'. To start out at raiding (which you are quite a ways away from) one of the best things you can do is level tailoring and use the Spellfire set along with the Spellstrike set. They will give you top-tier performance, especially in the lower raids, until a bit later when you (hopefully) start to progress into tier5 raiding instances.
Again, this is quite a ways down the road. Where you are at right now you will want to focus on 'of the Eagle' gear to get your int+stam in a nice little package and some spelldmg if you can pick it up to replace something if you aren't losing much of the aforementioned stats.
I hope this helps!