My advice would be similar to that above - don't start with a 125cc. Safety would be my biggest concern. A 125 may not have the power you would need to escape an emergency situation.
I ride an 800cc cruiser, but a 600cc sport bike would be more than enough to satisfy for a few years, and shouldn't get you into too much trouble.
Since you are new to riding, you are doing a motorcycle safety course right? I just started riding last year and took my course through the Calgary Safety Council. Within 3 weeks of riding, the emergency swerve maneuver I learned there saved my life.
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