Rushing IGGs in Colony games is very risky, because there's almost no way of catching up once the Colony player gets the lead.
In Province games, the IGG player can snag an occasional Province and hinder the opponent this way. Colonies upset this balance and not in your favour.
And Copper actually helps you when rushing IGGs, you need them to buy more IGGs and Duchies. 3 Coppers and an IGG, that's already a Duchy.
Steward is good choice since, if you can always play it, it's a of course better than a simple Silver. I would hesitate using it to draw cards though, more likely for $2 to reach $5 or to trash Estates if you're already on $5.