Hi,
I got married abroad (not Ibiza- sorry!) - so I have a bit of advice about planning rather than an idea for a venue.
You may need to get all your documents translated and legalised before you go - this does take time and of course money - so contact the spanish consulate for guidence.
Most holiday companies have a wedding department - they will help you with a suitable venue for your wedding breakfast, flowers, photo's and video - once your in resort you meet with your wedding planner who will talk you through what will happen on the big day.
Getting married on the beach.....
My advice is dont!!
There is nothing romantic about getting married on a beach with people standing around watching you with their swimming costumes on and inflatables tucked under their arms - or saying 'I do' to the sound of screaming teenagers playing ball in the sea!
We got married in a private gazebo just off the beach at 5pm and then we had our sunset photo's taken on the beach so everyone had left by this time - it was wonderful!
Whatever you do I hope you will both be very happy!
Joolz