Two questions:

Should I choose Defense, would this stop hindering terrain from giving the modifier towards ranged combat attacks? Put simply, do figures gain the hindering terrain bonus against ranged attacks when Defense is chosen for Communication Breakdown? I say no as the HTM is a modifier.

Secondly, No Action After Taxi applies to Amadeus Cho's Power Action Outwit, yes? I'd think so as it requires a power action to activate and NAAT prevents any action after taxi.

Thanks!

I would say yes on both counts. If Cho had true Outwit, he could get carried and still use it. But the wording of his power makes that impossible.

Yes on both questions.
Also don't forget that if it is a defenders team this will not prevent the replacement value.

Yep, replacement vs modify.

So basically Communication Breakdown is a one-combat-slot & full-game use of the Outsiders TA as it can slow down CCE/RCE/ESD and the like.

yes and no
It will prevent hindering terrain modifiers, but outsiders will not.
It will prevent the -2 from carrying where outsiders will not.
they are similar in some aspects but in the end very different. (other than one a TA and one a BFC.)

Specifically because Outsiders only prevents modifiers from powers and team abilities. Feats, terrain, BFCs, etc are free to modify.

Communication Breakdown does not specify where the modifiers are coming from (or not coming from, as the case may be), so all modifiers are toast.

Will CB prevent Thing's movement from being halved when charging? (Full Movement Charge?)

Someone better say no...

Okay: No. Halving is considered a replacement value, not a modifier.