Nicci is right on track.
Only, with regards to timing, I'd recommend the 2nd half of June or, if not, then mid September.
Don't worry too much about the DJs... there will always be people there you're interested in seeing (especially during those periods for the opening and closing parties).
If you're flying from Canada, not on a low-cost airline like of lot of our British friends, then it won't make AS much of a difference if you book 6 months or 2 months in advance. Just keep your eyes open for good deals to Spain and get a connecting flight out of Barca or Madrid on Vueling, Iberia, Spanair or Air Europa (then again, the cheap seats on those connecting flights could be full the later you wait. We're talking differences of 50eur each way)