Depends, I cant remember all the numbers, but I think it was something between 40 and 50 levels to get that build completed, the rest is up to the player.
But even if you focus those last skills on killing stuff, sooner or later you will hit a brickwall, especially on hell difficulty.
But the biggest problem with diablo was the ... how shall i put it... the lack of requirement for teamwork anyway. You dont have teams, you have several singleplayer builds in a group. You cant blame me for trying to turn the game into something interesting
Altough... with that healerthing in your party, especially the casters can get insanely strong, because they have a real hard time running out of mana even when they cast their most powerful stuff without any pause.
I cant remember the exact rules, either, I just know the meditation aura triggers a healing aura.
So first thing you do, is you get that certain staff you can build with some cheap runes, which, surprise, surprise, has meditation on it.
Then you can run another aura, yourself, on top of it. Not quite sure, but I think you cant just run meditation and have another healing triggered that way. I think you can have either 2x meditation 1x healing or 1xmeditaion 2xhealing active at any time. Dont ask me for details, there is some logic behind it, but its weird.
Of course the aura you run yourself could also be conviction, which is one of my favourites
Or lightning/fire/ice, but I dont like those, since you quicklly get useless on hell difficulty in 33% of the cases or so.
IIRC the most "efficient" build that gives priority to the healing and still has some kill power was one with conviction and this holy light thing, that shoots from above. Whats this called? The spell that goes "oooooh" in a monk-choral style. Not sure wether or not conviction lowers damage resistance against this spell, because I cant even remember the damage type of the spell.
Also, it's slow and "one enemy only" but it CAN get pretty powerful. But its kind of a tornup, you pour the skillpoints into the healing tree, and then you dont have enough to get all the synergies for this holy light thing.
Another interesting thing for healers would be the holy bolt thing, that can almost shoot at machinegun speed, because it heals teammates and damages enemies, especially undead. but I dont like it that you really have to AIM for your friggin teammates, so if I get it, only for synergies.