Trying to make it logical with the setup.
For Wano before Luffy arrives:
Zoro is leading the ronin of Wano along with one of the scabbards
Franky is in the capital, discovers through carpentry a secret access to onigashima, or manages to build boats to reach it. Onigashima doesn't need to be an island for the first part, it can be a fortress.
Usop really find hard to find him something useful to do, maybe he tags along with zoro and leads brigands.
Robin discovers the existance of the bombs and other crucial prisoners in the jail Possibly Yamato. It's key because Luffy is eventually gonna become prisoner here.
Arrival of Thousand Sunny:
Carrot drowns.
The arrival is fine as it is, Luffy finds that Zoro brigands are being under siege, during that battle he gets captured and brought to the fortress.
In the fortress Luffy learns to use the Ryou as he had, but in my opinion Luffy should have learnt this before being trapped, maybe he sees the fighters in wano using it, motivating also the SAMURAI ARE SO STRONG thing that has been built up for so long.
The more screen time comes from Freeing Luffy, the battle for onigashima is to free Luffy (Franky, Robin) to do, Sanji and Nami and Chopper to attack the second door of the fortress to avoid reinforcement to come in through the access, Queen fight ensues and virus shenanigans. Nami deals with fodder, maybe a tobiroppo. The virus is based on the Virus Virus fruit and chopper defeat the appropriate tobiroppo.
Jimbe, Brook and Usopp are to destroy the main gate, Usopp from the top of the gate has view of the whole inside mansion and snipes, a flying tobiroppo is his enemy. Jimbe can have normal fight, possibly Jack, so is Brook.
Zoro along with the scabbards goes to fight Kaido.
Supernovas are in an open field battle with big mom pirates.
Luffy is freed along with Yamato, scabbard are defeated but manage to take down Orochi, the second in command is a super samurai against Zoro. Luffy doesn't need to lose a thousand times against Kaido. Yamato role is expanded in the jail along with Luffy, where he things that she really is Oden along with the reader, only to be revealed at the end she is not. The role of yamato is weird and cannot fit here. The fortress start flying, momo becomes dragon to save it, Luffy defeats Kaido as the fortress becomes secure and momo drops it where the old castle was, to make it the new castle.
The end
