What is the Kingdom Hearts timeline?
Birth by Sleep > Kingdom Hearts > Chain of Memories & 358/2 Days > Kingdom Hearts 2 > Re:Coded > Dream Drop Distance > Kingdom Hearts 3

Why do Sora and Riku look younger in KH3D?
Because you are not playing as the true Keyblade wielders, you are playing as their dream selves and a popular theory is that the dream realm is trapped in the past to an extent. 

Why does Vanitas look like Sora?
Because at the beginning of Birth by Sleep Ven’s fractured heart connected with Sora’s, and in that moment the currently faceless Vanitas took on the face of Sora because there was still a lingering connection between him and Ven.

Where is Ven’s heart?
Currently unknown but my guess is in the Realm of Sleep.

When does KH3D come out in the U.S.?
July 31, 2012. 

Who all wields a Keyblade?
Sora, Riku, Kairi, Aqua, Ven, Terra, Lea, Xion, Roxas, Mickey, Master Xehanort, Vanitas, and Young Xehanort (D-Nort).

Who is your favorite character?
Male: Riku Female: Xion