Take note that each player in the game gets varied fighters every time they activate their Crystals. So aside from starting with a 1-star Optimus Prime (which you'd probably start to discard after you reach level 5), you get to choose your own way of pursuing the missions on each chapter, as the set of enemies in each chapter are randomized.
Game results may also vary whenever you encounter the splitting routes in every mission and the varied rewards you get whenever you pick the more perilous option. To get a better way of tackling the issues of strategy in the game, we would recommend reading the Tips and Hints page of this guide.
Nonetheless, here is a list of Chapters in every Act in the Story Mode which will give you an idea of how many missions you have to take and successfully turnover in order to progress in the game.
Chapter 1: Realities Collide
1. A Beast to Start
2. A Slow Learner
3. Me Have Mod
4. Good Cop Bad Cop
5. The Way of the Blade
6. Hail Who?
Chapter 2: Revelations
1. In Due Time
2. Anger Management
3. Don't Go Judging
4. A Scout No More
5. Loyalty Points
6. The Quintessance
Chapter 3: Shark Attack
1. We'll Need A Bigger Blaster
2. Appearing Act
3. Are You Not Entertained?
4. It's In Our DNA
5. Power Seeker
6. School the Sharks
Chapter 4: Under Control
1. Voices
2. Hold It Down
3. Code Violation
4. The Long Game
5. Optimum Outcome
6. Shackle Me Not