Yeah Episodd Ardyn is also the best one and the worst one. It really fleshes out the world but also clearly builds up to some alternate golden ending we never ended up getting that got put in a novel instead and completely undoes the themes established in the main game

But it is very cathartic. It also has a single episode anime prologue so I recommend checking that out

Also, are you going to be doing Comrades? If so I recommend doing it (or at least creating your avatar) before World of Ruin