I'd say 10 points or bust. The incarnate becomes incredibly powerful (along with the bone widow and the other summons, but the incarnate is the most diverse)
I had the same mage setup as you. As soon as my hydro/air mage could go 10 summoning, I respecced into it. I then geared him so I had 2 in hydro / air which let me use him as summoner / buffer + some extra damage/CC after he's summoned the incarnate and buffed that with farsight, power and haste. Gave him 1 pyro for haste and 1 geo for fortify. Once you level up a bit and gear up you'll have enough points to do both! I also gave my pyro/geo some points in other schools for Soothing Cold, Magic Armor, Tactical Retreat, Cloak etc.
edit: Oh and shackles of pain in the necro tree (coupled with living on the edge) is great for casters if you meet a mob with high elemental resistance. If you shackle the enemy and cast the spells on your ally instead, the spells will go through the ally's resistances, making it possible to kill for example fire slugs that normally absorb fire damage, with fire spells
Awesome! No worries! I just have one area left in Act 2, would you mind spoiling me on where you got the ring?