Greetings friends. So I just want to be sure about two things so I don't end up screwing anyone in a tournament.

SUPPORT Give this character a power action and make an attack roll (that is not an attack) against an adjacent friendly character as though making a close combat attack. When using this power, neither this character nor the target can be adjacent to an opposing character; ignore all combat value modifiers for this action. If the attack roll succeeds, roll a d6 and subtract 2 from the result, minimum result 1. The target is healed of damage equal to the result.

Would this mean perplexing up the healer's attack or down the target's defense wouldn't do anything?

And I'm pretty sure about this one but if say my figure (A) has 3 damage with two bolts and rolls a critical hit on both targets B and C, I can choose to put 0 damage on B and 3 on C and since critical hit increases damage to each hit character, B is dealt 1 and C is dealt 4, correct?

You are correct on both accounts.

Note that when using Support you can replace combat values via things like: Sinister Syndicate, Batman Enemy, Defenders, JSA, Defend or any ability that allows you to replace a combat value.

Correct on both accounts.

Jumping in with the crowd, yes you are correct with both things. The Critical hit with multiple bolts is probably my favorite thing that a lot of people aren't actually aware of.