Idea:
This could come with hubtitles for every 200 quests or so, up to 1000 quests.
Quest Addict
No Questions. Just Quest!
Quest. Quest. Quest!
Legendary Quester
Quest Master!
Maybe when you complete 1000 quests, you get a quest master skin!
It looks like the quest master, just a little different.
Credits zpc03
Not a bad idea, and I don’t really have anything to add to this but I’d like to bring some attention to this related post. Something like that could help display how many quests you’ve done. As for the prizes, see the Achievements section of my reply to that post!
Have a great day! 
Bump! This could add more rewards to dedicated questers!