I really like your suggestion for the multi-turn spells. That would be a really good addition to the gameplay.
As I said, multi-turn spells were quite common in the Infinity engine games. Though they were RTwP the system worked quite well. Casting times were one of the backbones of the combat systems of Baldur's Gate and Icewind Dale for a reason...

And I also like your idea of much higher action points requirements for certain very powerful melee/warrior skills. But a rebalancing is definitely needed here.
I'm a bit worried that we won't see the whole game before the final release. That way balancing issue in the late game won't be beta-tested before release...