New answers tagged tax-query
Set 'posts_per_page' to 1 on your args variable. I also suggest that you add 'page-attributes' while registering the magazine's post type and order the result by 'menu_order'. This way, you will have the field Order while editing a magazine, and set the highest which should appear on this query.
Taxonomy queries are by default extremely complex relative custom field queries. Without benchmarking I am pretty sure they are going to be slower even if the meta table isn't indexed, but you can add an index if you want. It won't effect WordPress at all. My advice is "use what logically works for the data". If you have problems, solve the problems then.
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