A High Priest who uses Holy Light is not a Combat Priest but a Holy Light Priest, lol.
If you're really trying to dish out crazy damage, I say go for the 300 INT (and wear a good enough staff that will increase your MATK) but I hate maxing out stats. You at least want to get your DEX to 150 (with the help of your equipment and if you want, Blessing.) Get good enough VIT because if somebody uses a Double Maya shield on you, you're screwed. Also, get a High Priest Soul Link so you can do more damage.
I can't recommend any good equipment because I haven't played in so long so I'm sure the cards I used are outdated.