Well... as a 25 healer going priest. I've tried many different builds and variations.
The best for me is.
3 MAG / 1 VIT
Oh, and as a healer to priest... no monster should -ever- be able to hit you.
Ever.
We have a skill that is based off of MAG that does X7 damage.
It's real good...
Pros about leveling as a healer-priest is.
You don't die. Or.. you at least shouldn't. You can kill mobs higher level than you with no problem. You never need to use a mana potion. Caster monsters SUCK. Since you get rohan crone 6 mag def per level. 

Cons about leveling as a healer-priest is.
Your staff hits for crap. Since you have no points in INT your staff does a lot less damage. Leveling is way boring, and it takes longer to kill mobs than it does for healer-templars. It sucks healing the whole party >:(!. Ohhhh and the attack skill you get rohan crone looks a lot less cooler than the ones healer-templars get. You don't get to use a +Physical defense buff because you're not INT. So you have to rely on good armor

As for templars... they're pretty much battle priests.
Nothing like an "elf mage" at all. It's practically a paladin...... a warrior+healer put together... almost.
They're -real- good in PvP. And a lot of fun.... and they look SO CUTE OMG!

hope this helped

Elf - Templar Build by Shin

Attributes: 3 INT : 1 VIT

Skills:
Healer

Heal 5
Divine Aura 1
Intelligence Blow 5
Holy Light 5
Emergency Heal 1
Mental Barrier 5
Teleport 1
Revive 5
Kill Time 1

I will fill in the templar skills when I get there :P

You will probably want to max Holy Light first followed by Intelligence Blow and then Magic Barrier. While doing this, you might want to up heal as you need it until it gets rohan crone.

You will also want to use a staff due to your high int.