One thing is for sure.
The longer the better.

And if Oda said 1000 chapters was what he was aiming for, that doesn't mean anything.
Most of the time it doesn't work out as you've planned.

And OP is such a huge story and a universe that has so much possibilitys that I think he has underestimated it.

He can't make 40 volumes for the first half of the GL and than rush things.
Ruffy has only beaten one shichibukai.
He has the beat the other ones, too. Plus the 3 admirals, BB, WB, maybe Shanks, plus some guys we don't even know.

Oda can't rush it and do it in a big brawl where Ruffy beats one shichibukai and Zoro, Sanji and Franky are each beating one too at the same time.

Ruffy has to put out the big guys and the rest of his crew the strongest underlings.

Not to mention the time faktor.
It can't be like "Remember Zoro. As we met I've said I'll be pirate king. Now six months later I did it".

It would make seem, becoming pirate king and getting one piece, like an easy task where it's supposed to be the hardest task someone can do.

Oda has enough options to keep the show entertaining for a long time.
Anything is possible in the land of sky islands and DF eating guns.
And he is still young. As long as he doesn't loose interest, everyhing is fine.

And if he ends up doing 100 volumes, I'll gladly read and buy them all.