You've probably already started, but since you probably didn't make too big a progress in a week...
Two invite codes there. I would suggest the one with the T2 Light Tank as the 500 gold is useful for other things as well. The Locust code is also pretty nice, but you probably can't take the best benefit of the week of premium in the beginning low-tier games.
Current Steam Name: Grilled Potato LF: Team Captain IRL