I'm sure RDD/PM/Sorc will be plesant to level up...</sarcasm>
Wing,if the barbarian side can do ANY good,then your magic sucks and you're better off without sorc levels. Same with CoT.
I don't think the percentages stack. I think it's more like Evasion in WCIII,where if you have 2 15% chances to evade,the game checks once then checks again. Taunting and Deafening a guy won't give him 100% chance to fail. It'll give him a 60% chance to fail,then he has to try again for a 40% chance or whatever the odds are.