I see act 3 being a mixture of Marineford and Enies Lobby with the Straw hats fighting their way towards the mansion and each better get a cool 1 v 1 against the numbers, tobi roppo, Big Mom's lesser kids, Oniwabanshu or Mimawarigumi.
the act ends with Law sending the scabbards into the feast and they get destroyed by kaido just as Luffy breaks down the doors to the mansion. If it follows the 7 samurai then at least 1 of the scabbards should die as the tragedy to end act 3.
act 4 is obvioulsy the big fights against Kaido, Big Mom, orochi, King, Queen, Jack, Smoothie and whoever's left from the groups fighting in act 3, the lesser straw hats should be ko'd during this time so they relaize they have to get stronger.
another few scabbards should probably die here too and the act ends somehow with kaido, Big Mom and Orochi being defeated.
Act 5 is the big party, the fallout, set up for next arc and leaving wano.