I think you're better off to book just the main cities that may book up quicker.
You don't want to book every single hostel in every city you plan on staying in, plans change!
The beauty of backpacking is you never know when you're going to meet up with a group of awsome people & completely change your itinerary
I've been a wild rover for many's the year,
And I've spent all me money on whiskey and beer.
But now I'm returning with gold in great store,
And I never will play the wild rover no more