There are already quite a few retreats such as :
Finca Colina Holistic Retreat Almogia Malaga Spain
Valle de Vida, holistic health retreat, Malaga
and a list at Retreats Online - Spain

So you can expect competition for a start.
I disagree with Chris above on international schools as if you want your child to go on to further education such as university back in the UK you might need the international standards to get entry.