If you get a decent pair of headphones then you don't have to listen to music too loud anyway.
When I first put on headphones the music doesn't sound to loaud but it's like my ears adjust and after a few minutes it seems pretty loud, even without adjusting the volume.
As long as your headphones cut out outside noise it's fine.
As for DJing though it's more difficult if you have really loud music pumping out & you are trying to listen to another track quietly