Current Zoro minus Haoshoku coating is roughly the version of Zoro King was ragdolling.
Serious, maybe. Zoro said that Luffy really underestimated him, so I don't expect it to be difficult.
Not sure no. But this chapter doesn't invalidate it.
If Saturn doesn't fight in this arc, his strength remains unknown, but I'd still think it's more likely than not he's stronger.
The Gorosei seem like EOS opponents IMO.
Borsalino falling first wouldn't change that all that much.