Journey fics tend to be long. The ones that follow the game plots (obtain eight badges, fight evil team, become champion) tend to be at least fifty chapters long, or at least the good ones are. Think of it this way. You want your character to be deep, to be well-rounded, to have gone through many experiences. Basically, you're writing a novel. It's going to be long. There's no limit on how long a fic should be, it's all up to the author's intuition. If you hit thirty chapters and realize that's only about your halfway point, that's fine. It means you've got another 30 chapters to go. See, don't think of chapters where no major plot events happen as filler. Filler means that nothing of any importance at all happens. Instead, make those chapters about character development. Simply traveling is not only boring to write about, it's boring to read about. So introduce or enhance a certain aspect of a character during that time. It will give you a focus, something to write about, and who knows, maybe become a major part of the story somewhere down the line.
This past year, I wrote a journey fic called Hero's Path that sorta broke the mold, I guess. There was no badge collection, no championship at the end. It was basically just a trainer wandering around the world, trying to find purpose in life. It ended up clocking in at 62 chapters, plus an epilogue. I wrote each chapter in a separate document, so I don't know how stacks up pagewise, but it was most certainly at least 350 pages long. Dragonfree's Quest for Legends, while I haven't read it myself, is completely massive. The best advice I can give is going to sound really cliched, but here it is: let the story write itself. It knows how long it needs to be, so just let it get to that length. You're just the vessel, putting it down on paper. When it's reached the end, it'll reach the end. You may lose readers along the way if it gets too long, it happens. Don't worry about it, you'll gain new ones. Just write however long you feel it needs to be written.