Hmm, there is no need to turn off spellcasting anymore. The AI has been fixed, no NPC will ever use aoe spells unless they are alone for miles. On my last playthrough, only a few weeks ago, I played through on hardcore without turning any AI off and I never had a problem. It's been tweaked a lot, I basically only used my main character (dwarven defender) and let the rest of the party tag along, attacking randomly. There's only a few fights in the game now that requires NPC management (such as the dragon).
If you want things to be easy, just make a solid party (example: Khelgar, Qara, Construct, Elanee, main char). Khelgar can solo most fights in the game, both as a fighter and as a monk.
General tip though: Never use damage over time AoE spells (ranging from blade barrier to various clouds) - NPCs will walk straight into it. Personally I only use buffs, heals, direct damage and aoe spells that only hit enemies (chain lighting etc). Better safe than sorry.
Edit: You can also select all characters at the same time now with a single button, or do a classic strategy drag-selection(such as in BG1-2). These features are available on mouse buttons 3 and 4, or 4 and 5 by default. You can probably change the key mapping for these new features if you want to.