Hi, I hope this is of some use. I have lived here for over 22 years now, married to a Spanish lady for over 40 years, and have seen many people in similar circumstances. You should check informally with the DSS in the U.K. as to if you can still receive U.K. benefit whilst living in another E.U. country. Should you have to rely on Spanish benefit then be careful as it is a lot lower and more difficult to qualify for. Heath care is prompt and good but the family here tend to provide for a lot of care for members when in hospital, nurses are not so readily on call and family members make up, watching drips and giving general health care. Work is scarce and obtained by networking within the family so one has to start making Spanish friends and building a network asap, if you rely on local expats you will find that many will be trying to do the same in a crowded market. Perhaps you could carry on with U.K. work over the internet.
Spanish SS costs for self employed are in the region of 250 Euros a Month, you will need to use a Gestor to help you with the returns adding to Monthly fixed costs, you then enter the SS system in Spain but need around 15 years of payment to qualify for the minimum pension. Regards Lionel