We need between 20 and 30 chapters if Oda wants to end Wano ASAP, so roughly three volumes. Just going off the fights and not any major revelations, Sasaki v. Franky, Who's Who v. Jinbe, Black Maria v. Robin and Brook & Hawkins v. Killer should take up a volume of space itself.
Jack, Queen and King's final fights all together should be another volume—about 3 chapters per fight with maybe King or Queen getting an added chapter or two.
Then dealing with Kaido and Big Mom? If you wanna be speedy, 5 chapters for each to be KO'd. And this is just a breakneck pace that ignores anymore set up, plot reveals (Momo will be doing this soon), pay offs (Momo's DF), Cipher Pol's instigations and Oda's classic "zero plot progression" chapters. God forbid Page1 and Ulti get back up, otherwise it's gonna be another 4 chapters for the duo minimum.
I'm guessing Winter of 2022 is when we'll be done with Wano.