This thread is fantastic, such detailed and interesting information! Really helps to get an insight into the production behind this episode and the anime generally! The animation this episode was sublime too! I can only imagine how much this arc will look in hindsight when it's over and we get to see everything animated by then!
I go back to WCI and enjoy scenes from it a lot more now and picking up new details here and there for example.
Queen vs BM has been so worth the wait in the anime!
Most of the stuff I know I get from being around people who follow the production of the show closely, or from directly following animators.
The animation director for this episode, and the sole animator for the second half of the episode, Tu Yong Ce, posted promotional art before the episode aired.
A lot of people who animate on the show do cool fan art as well. Its cool to follow animators just on the off chance they post some fan art they make for the show in their spare time.
Its a little sad the One Piece fandom doesn't really have any sort of well constructed sources that succinctly goes into detail about production aspects of the series.
I got into following the production of One Piece, funnily enough, through the dragon ball fandom, which although not overly informed, still has a banging forum page breaking down the production details of how shows are made.
It wasn't really that hard to transfer understanding of how a show like Dragonball super was made to something like One Piece(though its obvious that One Piece, production wise, blows a show like DBS out of the water, especially in its current state).
https://www.kanzenshuu.com/animation-production/
Other sites like Sakugabooru and animators corner are also good entry points, even if they are a bit hard to use due to how those sights are formatted(and aren't perfect sources either, a lot of the time due to the limited amount of shows they update).
http://www.animatorscorner.com/
https://www.sakugabooru.com/
Hell, other One Piece forums like Arlong Park, albeit less active, has a far number of members who are willing to take questions about this sort of thing(just be polite, a lot of people there are hard asses in some cases).
Its just a bit of fun really. Its especially fun if you have an interest in stuff like anime production, or art more generally.
Learning about how anime is made gives you a better appreciation of what goes into a show. For example, this episode, an animator who was also animation director, solo animated half an episode. Knowing a little bit about production can give perspective to how impressive something like that is.
Yeah, you can still be critical. But it allows you to be critical in more constructive ways(I for example, do not like particular animation directors because they've historically had rather iffy character art. The most well known example being Toshio Deguchi, who is generally not fondly regarded by people in the know). In saying that, do not use production knowledge to personally attack the staff on the show or try be too picky with them.
Anyway, I think that's enough of my fairly episode unrelated rant.
Also, a few people I am in a group chat in translated the animation credits for the episode. Typically, Toei handles animation credits by having the person highest up on the staff list animating the most cuts, with those at the bottom animating the least(there is some discrepancy based on how staff credits are shown between studios, ie, some shows may give second key animator credits while some don't). Its also important to note that some key animators do end up going uncredited(though the only time that may be relevant is in the context of a really well animated scene that is obviously done by an animator who didn't show up on the staff list).