I have the west versions of Yakuza 3,4 and Dead Souls, and the Japanese versions of 1&2 HD and Kenzan. I’m buying Ryu Ga Gotoku 5. When I start to play it, it will identify the american save and give me the bonus itens?

Probably not due to the naming schemes of the save files internally on the PS3. Any bonuses you get from the HD version or Kenzan should work though!