So I own about 90% of the game's available product and have only played the base campaign once as a Rebel and 4 or 5 skirmishes. In short, I'm drowning in product and short on knowledge. So, my query, for more experienced players is, as anoted upcoming Imperial player, which classes and Agenda sets should I look at/avoid? I know a comprehensive list, at this point, is asking a lot so anything would be helpful. I tried looking online before posting, but all I found was a post on BGG dating back to the core game. Any help, advice, or whatever would be ultra appreciated.

What campaign are you playing? With regards to class decks, I think there are some pretty good articles on this forum that have some good discussion about the various class decks:

I would encourage trying a different class deck than what was used in your previous campaign. Also, depending on the outcome of your previous campaign, you can adjust the difficulty of the campaign by playing either a stronger or weaker deck. It is more fun to have a competitive game than a one sided stomp so that is something to consider. Since you get to pick the Imperial class deck after the Rebels pick their heroes, you can use that to your advantage as well - some decks will perform better than others against certain heroes.

Regarding agenda decks, most of the decks in the core are pretty solid.

I would suggest picking a couple strong agenda decks and then pick a few for fun or ones that seem thematic with the campaign.