Basic minimum Requirements imo:
300-400 all res
I also use the Templar with 100k HP
Build : http://eu.battle.net/d3/en/calculator/wizard#blXRmO!aYT!bbabZY
Basic Venom Hyrdra Blizzard build
So Phase 1 is the easiest once you get it down right. You just blizzard a path to the far right hand side of the room, set a hydra down. Then make sure you always keep a blizzard on you, and one just in front of that one. Then spam Shock Pulse, whilst keeping the Hydra and Blizzards up. If any mobs start their swing, crystal shell.
Once I got this right, I never got hit once in phase 1, and it was a breeze.
Phase 2, the usual problem is that Belial falcon punches your face whilst the sentinels are also ramming their sticks up your behind from all directions.
Basically I used the Templar as block for everything. To start I drop a hydra and blizzard, then I just move so that the Templar is always between me and Belial. This way Belial will always melee the Templar first.
As soon as Belial starts his green waves of doom, you archon and spam him with its disintegration. The templar usually soaks up one of the waves, so you can literally stand still, since the mobs don't spawn till after he's done his first green waves. He'll be pretty low at this point already. Archon should last until mobs start spawning, and you can usually move behind the templar again, or just teleport and 1shot the ads to keep up archon. If archon drops, just blizzard+hydra and run about until phase 3, which should be pretty soon. Use Diamond Skin if you mess up your position, and Belial is about to punch you.
Once I got this regular, I again didn't get hit once.
Phase 3, is much easier than Phase 2 I think. You basically just drop hydra and blizzard and keep moving. Stay around the far right, so you avoid every breath. And just keep moving, you'll get used to where he does the punches eventually. Save Diamond skin for if you mess up and are about to be hit by the double punch, which can basically one shot you. Normal punches you can use one of the many health globes that will appear.
Safest time to Archon if it comes back on cd in p3, is when he breaths, since after he'll be doing normal punches 3 times before the big double one.
So yeah, doing it this way, I killed him in 2 tries. You can probably do with lower stats, it will just require you to not make any mistakes, obviously less HP means less room for error, but if you get more damage out of it, then the fight will be quicker.
Anyway , good luck.
arcane orbs are nice, hit hard and actually stun them slightly on hit combo'd with temp flux adds didn't last long, and i archon then in p2, i nuke with orbs until he casts his blasts then pop arch, and it went down really fast, then its just a matter of dodging the stuff while keeping hydra up and occasionally orbs, make sure you have movement speed though or you got no chance.
What I can't believe is that some people are asking to pay gold to get past belial. Challenges are the best things about the game, and overcoming them. I didn't find too many good guides to do Belial when i searched on the forum, which is why I made this. Once I used the Templar for p2, it was really easy.
My templar, I just stacked vit on every slot to get him to 100k hp. so like 200vit items with any str on them. Was pretty cheap to buy. Skills I just took his taunt/stun etc, his heals dont do much, but I guess it might save you a couple of times when waiting for Diamond Skin/Potion cooldowns.