Dude they are totally already friends, Aqua is in the group of KH protagonists who bond with others with ease (she's like third place after Ven and Sora)

BUT YES SPARRING PRACTICE and come to think of it, Aqua's combat style is probably the closest to what Sokka would know out of the KH canon since she's definitely a finesse lady when it comes to physical strikes rather than bludgeoning.