I would book the hotel as soon as possible, I'm sure there will be room for you, but you're always better safe than sorry. (You can always change the reservation if you decide to go off of your schedule!) The Alhambra tickets I'd just buy when I got there. Also, if you're going to be in Granada on a Sunday, there's free entry into the Alhambra at least until 3, if not all day! Have a great trip!!
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"Vivir con miedo es como vivir a medias."