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If you are a UK or EU citizen then you can go today and stay as long as you like or at least until you still have money. You'll need to get a residence card - from a police station, this essentially will prove you are who you say you are, and although not compulsory will help with paperwork, getting a doctor, opening a bank account etc.
Above all learn the language, once you've done that you'll be able to study - if a university or college will accept you, get a job etc. I imagine there'll be a lot of bar/tourist jobs going in the summer and that should get you started. Regarding a proper full time job, there is no reason why you shouldn't work. You will have to get registered with the Spanish social services etc and pay their taxes etc, but again you need to learn the language.