YES! eveybody has one, even if they don't believe in them!
The real Alison.
No. Xehanort's Heartless (the fake Ansem) looked like Ansem the Wise (the real Ansem) but a lot tanner.
Emblem Heartless are artificial Heartless created by Ansem the Wise for his research on Heartless.
Well, because Xion isn't a real Nobody, she doesn't have a Heartless. Xion is merely a puppet created from the leaked memories of Sora during the events of Kingdom Hearts: Chain of Memories.
Multiple heartless are heartless! Just like fish or sheep.
Bullies are heartless. Heartless comments hurt.
No trees are heartless.
No. He is not a heartless, and never has been.
Sora's Heartless was Pureblood, since it was neither created by Ansem the Wise nor marked with the Heartless symbol.
Yes, he was a real character. Whenever someone is turned into a heartless, a new person is created. This is the Heartless' Nobody. Sora turned into a Heartless for a brief period in Kingdom Hearts 1. This is when Roxas was created. Roxas, in basic terms, is the other half of Sora.
Technically neither. Xehanort became a Heartless, and that Heartless called himself "Ansem."
Emblem Heartless are not a new form of Heartless. They are creatures that bear the insignia of the Hearless. Unlike the Shadows, these Heartless extinguish hearts when defeated, whereas creatures such as Shadows or Neoshasows are Pure Heartless and do not realease a heart.