Oh. Oh no. Oh dear GOD no. It's going DOWN.

This implies that Zoro has more base HP than Luffy right?

Not an unreasonable guess. Luffy was designed to make use of secondary mechanics to mitigate damage, like monstrous DR and immunity to bludgeoning damage. If you don't take a lot of damage ever... why worry about a big HP pool?

It seems reasonable based on what we see in this series. Though that said it's not like Luffy is short on HP either.

Given what happens when they meet Kuma... Yes, yes he does.