I'm at 49/50 Isabel (Isabelle? I wish they'd proofread at least on important stuff like character names.) shards from farming just the easiest stage. I'm unable to complete the second stage...maybe I'm doing something wrong but the trash mobs on it take a good chunk of my HP before I even get to the boss. I couldn't even cheese it with a high-level ally.
Doing it this way won't be for everyone, because I've sunk every single AP since the start of the event on that one fucking stage to get there, but it can be done. But on the plus side, I've got nearly every character maxed from all the books.