Thanks for posting! I'm glad you like our forum
I'm also really impressed that you posted your own explanation - this is exactly the sort of thing you want to do to be achieving mastery.
I'll take the time to go through each answer choice as you describe it and thresh it out a bit more for posterity/other users of the forum.
First, just to label it, I'd say that the conclusion of this argument is not necessarily spelled out. Tell me if you disagree, but I think the conclusion is really the implied one that the magazine's message that most local residents opposed the exhibit was not necessarily correct.
(A) You said this answer seemed out of scope given the conclusion, and I agree. "Special expertise" knocks this one out.
(B) You also said this answer seemed out of scope, and I agree too. We don't know anything about whether the population is "likely to be evenly divided."
(C) I would say that this answer has a scope problem just like (A) & (B). There's nothing wrong with sometimes including an "unless" even if there isn't one in the passage (such an answer wouldn't be likely to be the anwer, but could be...), but here it's also the condition the "unless" introduces - that the opinions they express are widely held - that we know nothing about. It's just as much out of scope as (A) or (B) because we know nothing about whether people agree with these 3 friends. In fact, that brings us back to the central problem the argumetn is pointing out!
(D) You said the argument does not imply that the friends must agree with each other, and you are dead on. This again is close, but no cigar. I'd mention as an aside that C and D were probably the smart ones to save for last other than...
(E) Here too you were dead on. The issue is that these three friends are potentially non-representative of the group - they seem to be a cluster of friends, so they would be presumptively unrepresentative unless they are an unusually diverse group of friends or it is an unusually homogenous local population.
I am not sure what you meant by TCR, so let me know if there was an additional question. Otherwise great job! I'd love to see more of your explanations if you feel like writing them up