definitely do it mate, you won't regret it, as for tips, same as Stivi said above. Save as much money as you can, don't forget, when you're paying rent you'll need the rent plus another months rent upfront as a deposit. Money goes fast over there, very fast, I know a couple of people who left in June/July because they blew all their cash in the first month (some even before that). It is about €700+ for studio, but if you want to share with other workers, you can rent a room for around €300 per month, depending on where it is.
Job wise, just walk around all the bars etc asking for work, be careful of 'free trials' with a promise of a job at the end of it, I was conned with that one, doing three days of 'free trials' and when I asked about a residency was told "why should we pay a resident, when we have loads of DJ's coming in to play for free?".
Also don't expect to only play the music you want to play, I had to play Funky Flares (RIP) three nights a week to cover my rent, although it was owned by Eden at the time, so technically I was working for Eden
then I was able to play the music I love regularly at other places, V Club, Hush, Kanya etc.
It's hard work and sometimes you feel like you wanna get the next plane home, but the people you meet will be some of the best people you can meet, and Ibiza is the greatest place on earth.
With regards to the NIE card, you pick the forms up from the police station in Eivissa Town (near the McDonalds) take it to the bank to get stamped, this will cost you €10.20, or it did in 2012, then you take it back to the police station on the date you were given, and you get your card, it lasts for 5 years apparently, by the time I got my appointment, they had changed the rules saying everyone needed a contract to receive their card, so I didn't get mine. I am gonna look into getting it from a Spanish consulate as mentioned above, as that seems a lot easier.