Locke the Treasure Hunter, or maybe Relm with her potty mouth, might fit Scout a little better than Gau. Maybe Mog, if we're going for the "diminutive size" angle.
And Cyan seems more like the Sniper's than Soldier's personality to me.
Setzer could be Demoman, drinking his sorrows away.
And Umaro as Heavy could free up Sabin to be Soldier.
Edgar as Engineer is obviously perfect though. And I love how the only difference here is that you added a blond ponytail.
Terra as Medic and Celes as Spy also fit well.
And Gogo as Pyro is a hilariously good choice.
5'd