I think you will find that re-plating a UK car to Spanish requirements is still pretty expensive ... it was when I did so 9yrs ago, and I doubt that it has got cheaper! You'd need to change the headlights, and possibly the reversing light, pay spanish import tax, registration and ITV costs, the thick end of 750-800 euros!
If you are ONLY coming for a 12 month visit, and then returning to UK, I do not think it is worth doing.
I personally would either buy a cheap Spanish runabout, or bring my UK car, with valid MoT if relevant, insurance, and plenty of evidence of your being a UK resident ... eg UK driving licence, utility bills etc ... and take a chance. If you are stopped by Trafico, for any reason, soon after arrival, say you are a visitor, and then take the car out of the country after <6months, and then return for the remainder of your year.
It's a small risk, IMO, but the fines can be heavy. However, again IMO, 'importing' a car is a heavy price to pay, if , as I said, it IS 'only a visit'.
It was justifiable for me, as I'd only had my car a few years, it had several expensive 'extras, and I would have lost heavily on selling it in UK, and then had to pay-out a bundle for an
unknown quantity in the shape of a Spanish SH car.(And I actually prefer a RHD car, even here, and find no difficulty driving it on the 'wrong' side!)And what would you do with your (presumably RHD) UK car, on Spanish plates, after 12 months? It would be worth little here, and more expense to re-register it again in UK.
I believe the driving licence issue is definitely not worth worrying about, for such a time(unless your 70th b'day falls in that period) .... it could take you most of the 12 months to get it changed !!!
I have tried twice, the first time just before my 70th b'day, and I never received my Spanish licence! A few years later, still driving on a renewed UK one, I tried again, in April this year ... I am still waiting
(But I carry the evidence of having TRIED!!).
I hope this helps ... beware, you are likely to get much conflicting advice on this subject ... this is just
my experience and opinion!