TAMAKI
-Ever since the live-action project started, Hatori Bisco, the manga author, immediately nominated Yamamoto Yusuke to play Tamaki's role. (DOGATCH & +act)
-Tamaki's hairstyle and color contact lenses, were Yusuke's original ideas. He suggested it to the production team, and were accepted. (JUNON)
-Yusuke almost never watch the anime, so his portrayal of Tamaki is not based on the anime. If it's similar, he said it's just a coincidence that his patterns of thinking is the same as Tamaki so he reacts to things the same way. (DOGATCH)
KYOYA
-Daito chose his own glasses, which he thinks suit Kyoya's character. (JUNON)
HIKARU & KAORU
-In the initial audition, when Manpei-Shinpei were asked, "Which one will play which?". Both of them wanted to play Hikaru. But as they read the script, Manpei agreed that he has some resemblance with Kaoru. (JUNON)
-Manpei is basically more like Hikaru in real life, so he needs to build/makeup Kaoru character, unlike Shinpei who can act Hikaru with his natural-self.(JUNON)
-Manpei also used Anime-Kaoru's voice as a reference to create his own LiveAction-Kaoru's speaking tone and voice.(JUNON)
HONEY & MORI
-They were rehearsing the fight scene in Ep10, under the supervision of a real karate and kendo teachers, and it took 3 hours just for the rehearsal itself. (MOVIE GALLERY in Official Website)
OTHERS
-The whole Ouran cast had manner lessons taught by a teacher from the Ogasawara School of Etiquette. They learned greetings, how to drink tea, and gestures. Daito actually used alot of the lessons he learned to act and build Kyoya's character. (JUNON)
-Hatori Bisco nominated Totsugi Shigeyuki to play Ranka, Haruhi's father, and the producer accepted the idea. Bisco is a fan of the actor. (twitter)
Please remind me of the other interesting facts!^o^