Take note that each player in the game gets varied fighters every time they activate their Crystals. So aside from similarly starting with a 1-star Optimus Prime (which you'd probably start to discard after you reach level 5), you get to roll your own way of pursuing the missions on each chapter. Game results 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 on the Tips and Hints page of this guide situated on the Table of Contents on the right.
Nonetheless, here are the list of Chapters in every Act, in the Story Mode, to get you an idea on how many missions you have to take and successfully turnover in order to progress in the game.

Chapter 1: Secrets
1. Echoes
2. Butt Heads
3. Who's Your Master?
4. Scout's Honor
5. Believe The Mirage
6. Machinations

Chapter 2: Quintessential Quintesson
1. Spy Games
2. Just An Illusion
3. T-Cog Probs
4. Origins
5. Dear Diary
6. History On Repeat

Chapter 3: Into The Darkness
1. Warriors At The Gate
2. Join The Army
3. Miner Relief
4. Insecurities
5. Head Gamezzz
6. No Petty Relic

Chapter 4: Treacherous Returns
1. Are You Not Sentient?
2. By The Blood Of Unicron
3. Descent Into Depravity
4. Who's Superior?
5. Assurance
6. And Then There Were Five