It seems this Third Act is about Introducing both Sides in detail before finally War starts (Act 4) and Post-War Epilogue will be short Act 5
We had Oden's Flashback, Reveal of Traitor, Three Supernova Captains arriving, Samurai arriving with Denjiro joining, Jinbe arriving, Introduction of Flying Six, Return of Apoo, Neko's return with Marco & Izo and we have few Clashes here & there & each group taking a Position
The Pattern is clear here, Introduce all Players & show where each one Stands in both Role & Location
So for Next Chapters, i expect Introduction of All Numbers, Introduction of Yamato, Calamities & Ninja/Samurai Groups, Neko & Izo reuniting with others, BM Pirates late arrival & maybe Hiyori appearing somehow + Hawkins of course
Most probably we have around 6-10 Chapters before this Act ends making it around the length of Act 2