That is not a bad build, but I would make a few suggestions. By maxing FM and FB, you are committing to fire being your main attack. This being said, I would not max cold mast. I would spend a few points there and let + skills raise it, investing the other points in Firebolt (another synergy.) Basically, fire is your main attack, with orb as a backup for fire immunes and a method of slowing monsters to keep them in hydra.
Depending on what you are planning for this character, 1 in ES might be plenty. I have a hydra/orb sorc that I use for MF. 1 in ES and 1 in Chilling Armor helps her get thru the durance of hate without dying as she teleports around the outside to lvl 3. I have to drink a blue pot now and then, but I am damned glad for it when I tele into some might enhanced dolls. I'm not saying you have to do it exactly the way I did, but I can say that the build I use is effective; she finished the game with no rushing, and soloed baal at lvl 78 with some fairly mediocre gear (occy, shako, smoke, and garbage.) Feel free to PM me if you'd like any more info.