Good morning
in order to fly UK or EASA registered airplanes as PiC you would need a license from those countries so… conversion would need to be done first (UK may have a different view and/or exceptions but EASA is clear about it)
to convert your AUS PPL to EASA you are required to have the license and medical current… and hold at least 100 hours (Spanish CAA require certificate of hours to be with The Hague Apostille
you would need to study carefully what makes more sense from a financial point of view (if you were in Australia now… it is a no-brainer)
your AUS flight hours will count towards the requirements of a CPL license (200 total and 100 PIC)
Best of luck with your process