Yes there can be only 1 hero the rest play a supporting role.You have Messi the team is built around him.
And yes i think you can pick a random player in the TM and make him a Superstar by giving him the training and making him the highly rated player in your team. Ofcoz have to be Aml/Amr very rare a St.
I make my to be a superstar Maradonna and have to sacrifice my top scorer Lauretta. Bought him at 18yo and now he is 21.

Sent from my SM-A800F using Tapatalk