Picture a Gundam, maybe slightly smaller; that would give you a good idea of the typical height of Gareth; however, he can be made taller from the sheer bulk of armor than can be applied to him. I think Leona's mech is about the same, and I'm not sure about the others. As for the logo, I like it! If I was even a halfway decent artist (I struggle with stick people), I'd draw it.