You get another one via a wartable operation after the Wicked Eyes and Wicked Hearts quest if you reunite empress Celene and Briala. I'm pretty sure 5 is the max (+1 for human).
Nice, didn't know that - thanks 
Defensive okay Knight Enchanter take two.
Spirit and Knight Enchanter Abilities.
Race: Qunari. Melee defence is useful.
Knight Enchanter: All abilities spent. [11 abilities]
Spirit: Everything except mindblast and strength of spirit [9 abilities]
Winter: Fade Step and Upgrade [2 abilities]
Inferno: Immolate (without upgrade) and Flashpoint (so that I can keep casting) [2 abilities]
24 points.
If there are even more points (maybe from DLC), I'll use them to get clean burn from inferno tree and max out the Spirit tree.
Clean Burn should be very high priority, imo. One of Spirit Blade's main functions is to work with Clean Burn to reduce cooldowns on your harder-hitting abilities.
I've never found it necessary to take the entire KE tree, mostly because I think Disruption Field is of questionable value.
It's definitely not necessary to take most of the Spirit tree, either. The only thing I'd say is essential is Rejuvenating Barrier. But if you're just going to spam SB and Fade Cloak all day and never cast anything else, that's not even needed. Barrier upgrade and Guardian Spirit are definitely a waste, in my opinion.
The classic "core" build goes something like:
Spirit (4): Barrier, Peaceful Aura, Dispel, Rejuvenating Barrier
Storm (2): Energy Barrage, Conductive Current
Inferno (3): Immolate, Flashpoint, Clean Burn
Winter (1): Fade Step
Knight Enchanter (7): Spirit Blade+, Fade Cloak+, Combat Clarity, Fade Shield, Knight-Protector
That alone should let you beat just about anything by using Fade Cloak and spamming Spirit Blade until it's off cooldown. It's 17 points, so you have many others to play with in terms of how you want to deal more damage and make things less boring. I personally like the Fire Mine route (Pyromancer/Chaotic Focus/Fire Mine+), plus upgraded Energy Barrage, Fade Step, and Dispel.
Also, fyi, as a Qunari you can get up to 5 additional ability points.