Heya thank you for checking out the game.

1. Yup each of them have distinct play-styles. Like each of them have their own set of attacks that can be used situational (crouched, grounded and mid air). Depending on their class, they each have their own attack, mobility skills and dodge skills. Each character also have their own storyline each with their own ending depending on the choices you make. And some choices affect what will happen in the other character's storyline too. There are multiple endings in the game and there is a true ending.

2. There are 4 game modes. Each of them can be played single player / co-op.
Story mode - Will let you play the four character's storylines. These stories will let you know about their backgrounds and reason for coming to the Tower.

Arcade mode - Let's you play the game without the story. Good for casual boss-rush runs. This gives you 3 lives to spend, after that it's game over and you have to start again. You get to fight the main bosses of the game here.

Free Mode - You can play any of the levels you have unlocked in story or arcade mode. It means you're the one choosing the levels you're going to play on.

Boss-Rush - It's an unlimited boss rush mode where you fight all of the bosses in the game until you die.

Hope that answer's your question. :D