Newbie Questions - Becoming a Resident

Hi all,

In the early stages of looking to shimmy on over to Barcelona. From London, currently living in Malta.

Very much aware that I am going to need to be settled by the end of the transition period for Brexit. So ideally I hope to have my feet on the ground by October this year.

I suppose my initial question is if anyone answer, what exactly will I need to prove I am resident? Here in Malta for example we need to provide ID, passport photos, tenancy contract from landlord as proof of address. That is then processed which takes around 6 weeks and you are then given an ID card with unique number. Effectively an resident card.

Anyone shed any light on what is needed and the process I would need to follow plus time frames to complete?