Sorry but it's likely that this won't be completed but I will share with you the plans I had for the story:
At Casino Nights; Raza would have invaded an destroyed everything and take the Chaos Emeral from Clutch.
Sonic would have pushed back Metal Sonic.
The bad guys would have gotten the Chaos Emeralds but Robotnik betrays Raza using the Chais Emeralds vest using the power of entropy him and claim them himself. Sonic, Tails and Knuckles would have gloated to the stunned new friends by doing their dance from earlier.
Sonic would have confronted GUN about Metal's creation and Randall and Sonic would have a heart to heart. Randall revealing that he lost lifelong friends in his squad when they were compromised during a mission; a mission that failed thanks to Sonic's energy surge from the first movie. Sonic realises consequences for his recklessness and still not too happy with him, understands Randall a bit more.
Robotnik uses the Emeralds to build the Death Egg.
Seems hopeless for the heroes but Knuckles trying to motivate everyone with a speech that is a patchwork of disconnected verses from famous movie speeches with no lime or reason. Just confuses everyone more than it inspires them.
The heroes uses the Master Emerald with them as they use ships to get to the Death Egg. Robotnik is defeated but an upgraded Metal Sonic is the final boss with it and the station blowing up.
Sally gives Sonic a kiss to celebrate the hero and the story ends with everyone at Sonic's birthday party.