Lol i told a huge amount of info i already gathered up about KH3. Ill try to summarize it and put sum info u guys probably never heard yet.

Yes, KH3 is a prequel to the past before Sora, Riku, or Kairi. Those people u see in armor are called the Chasers, the brown haired chaser is named Terra, blue haired is Aqua, and the one that has a great similarity to Roxas is Ven.

Each of these names have a connection with the main characters.

Terra = Earth Riku
Aqua = Ocean Kairi
Ven = Wind Sora

They also put little hint to symbol that it was the past by showing Mickey with the Starseeker keyblade, this was the keyblade Yensid, who was his teacher on how to use the keyblade, to practice on.

What else.....well.....that old man was wearing the clothes of Ansem or Xehanort's heartless....and the shadow figure he summoned was wearing the clothes Riku wore to get the power of darkness.

I cant remember what else right now.....ill try to keep u guys updated