Jack as a mammoth zoan is probably confirmed (he may be an artificial zoan, though). Him being Kaido's underling is definitely confirmed now. Sheepshead referred to him as being one of the three calamities, which makes me wonder if the calamities are Kaido's strongest underlings (possibly including Kaido himself?) or just three beings generally known for their destructiveness regardless of affiliation. Probably the former, if I had to guess. I wonder if X Drake is one of these calamities?
So the Gifters group are probably made up of artificial zoans, but is Sheepshead the strongest of the group? Being that he was beaten by Sanji with relative ease, this army of 500 zoans Kaido has doesn't seem like much of a threat anymore if so. There's also a Pleasures group, whose only purpose seemed to be to get crushed by random Mink civilians and show off their Electro power.
Oda has been introducing us to a lot of minor characters ever since the start of this arc, such as Sicilian and the whale forest guardians. Given Sicilian is only one of three musketeers working under Inuarashi while Nekomamushi is likely to have his own elite guard, it seems like this is going to continue. Hopefully this is because they're going to play an important role later, but given that we just had something similar happen when loads of characters were introduced for Dressrosa it has me concerned.
I still can't tell what the conflict of this arc is going to be; I just hope that whatever happens is actually important to the Kaido story Oda's been building up. I don't want to see a lengthy contrived conflict pop up just for the sake of giving the crew something to do on Zou when the plot could be moving on instead.