I don't think that the Merry really has any kind of Klaubauterman yet, I think it's mostly just a gag as the ship is too new and they're still trying it out.

Yes, Luffy is self-centered. I think even if he knew how much it cost to repair, he'd only work the amount of time he wanted to work. There are plenty of examples of him being a self-centered kid-- but no one said he was a hero. He does what he wants.

You may be right about the last though. I'm not sure what was on my mind when I was thinking it because Sanji is pretty cantankerous when he gets riled up--which is probably often? But he holds back a lot here, too so maybe he has more control on the Baratie. (but not by much) It's definitely something I'll have to look at in future installments.