How many playable characters are there in Tales of Destiny 2?

Do you mean the actual Tales of Destiny 2 (PS2) or Tales of Eternia (PS1)? ToE was renamed to ToD 2 for unknown reasons when it came to the US.

This is ToD 2.

http://www.youtube.com/watch?v=b__wFt8YLQk

ToE has around six playable characters.

Reed (Rid actually), Farah, Meredy, sciense-guy, crazy bazooka guy, and the little pirate.

You'll see Farah in Symphonia in the cameo battle.

You'll see Reid in Abyss in the cameo battle.

You'll see Nanaly, a character from Destiny 2, in the cameo battle in Abyss.

Oddly, we still didn't get a port of Destiny 2, but Destiny 2 character is an cameo battle in Abyss, which got ported.

Cast of Destiny 2: http://en.wikipedia.org/wiki/Tales_of_Destiny_2

Cast of Enteria: http://en.wikipedia.org/wiki/Tales_of_Eternia

Just go to character section from both link to get a list of the cast.