Since there is a recessed light where you want the fan, you know there isnt a joist there . . . so install a fan brace through the hole. Mount the fan to the brace, and use a medallion to cover what the fan’s canopy doesnt.
May I recommend using a an industrial/commercial fan. They have metal blades, expoxy finishes, and move more air more efficiently than residential fans (especially those designed for outdoors which have heavy plastic blades). They come in 36″ 48″ and 56″ size, and some companies offer a 48″ light kit adaptable fan. More information is here:
http://www.ceiling-fans-n-more.com/industrial-and-commercial-ceiling-fans.php
Good luck!