For the role of an interior designer specializing in planning spaces and creating ambiance, I would suggest casting someone with a keen eye for detail, creativity, and a passion for design. This person should be able to think outside the box and not be afraid to take risks in their designs. To overcome the challenge of staying current with ever-changing design trends, this individual should constantly educate themselves, attend workshops, and collaborate with other industry professionals. By staying informed and open-minded, they can continue to deliver fresh and innovative designs to their clients.