To get new characters all you have to do is play arcade mode with the original characters and win all eight battles.
After you enter your name in the records (if you qualify) the screen will say "A new soul has arrived." Or "New travels await."
This is a list of all characters you can get.
Hwang, Lizard-Man, Cervantes, Yoshimitsu, Rock, Siegfried, SeungMina, inferno, and the Edge Master.
Also by playing Misson Battle you can get new costumes, weapons, stages, character profiles, and gain new modes in the museum when you buy art. (If you are looking for anything I just named you want to buy the most expensive art first.)