It would be worth using the services of someone who does this for a living and is totally au fait with the system. There are so many forms to complete at different offices and so many hoops to jump through that is it is quite difficult to understand. Also, if your Spanish/Catalan is not great then you will have more delay. I have recently re-matriculated my Mercedes from UK to Spanish registration and it took about a month using the services of a gestor. I used an English guy called Robin Williams, phone 636104592, and he was great. The whole process (including import tax of some €350 because the original cost price of the car was high) cost around €850 including Robin´s fee. I did want to do it myself but really, life is too short and Robin does this all the time.
Cheers,
Simon Smith