Current page number is 6841
So, quite long, and we're only on Act 6 Act 2... out of 7.
Hussie said it would be around the size of Act 4, but he has since gone back on that and now it seems like it might get even longer than Act 5.
As for the Gamzee/most important character thing... the main theory is that it refers to Cal, who Gamzee was holding when that quote was dropped. Cal has been present for pretty much every major event after all, and is also part of Doc Scratch and Lord English.