As a starter I would suggest you take a look at
plus possibly other threads under the driving in spain thread on Spanish discussions, there has been lots of advice on this subject.
MOT will be no good as Spain has an ITV and you will need to change lights as well as re register the car at the local Trafico office but worth employing a Gestor to advise you.
It will be illegal to keep UK reg car in Spain indefinitely
For insurance try Linea Directa, very helpful.