Re: Delaying an opponent
I have not played COH in a while, so I may be wrong, but I thought stunning in COH dropped your toggles, which is similar to the effect in Hero, so I’m not really sure how what your trying to simulate is different than being stunned in Hero. Having said that, being stunned in COH does not seem like quite like the death sentence as it is in HERO, although I think this is largely because, as stated earlier, stunning someone in Hero normally means they have very little stun left, in COH you may have a bunch of health left after the hit that stuns you. If you started adding extra damage only to stun in your campaign, these stuns would start to come when the characters still had stun left to them.
You may just add a new mechanic or power called daze that causes a character to lose part or all of there action based on damage, or dice in the new power. If a character takes damage equal to x% of their CON (or EGO) they are dazed and lose ½ a phase, but their DCV and non-persistent powers are not affected. You could have multiple levels as you suggested, but multiple dazes should not stack.