Does a step-down voltage converter draw its maximum wattage
If you have no devices attached to the transformer, it will draw very little power depending on the transformer core design, a few watts at most. When you attach a load then the transformer, as its name implies, will transfer power from the input to the output.  It will only transfer as much power as the attached device needs.  If the device only needs 200 watts, then that is what the transformer will deliver. The 1000 watts is the maximum power the transformer is designed to deliver safely. You should not exceed that value, probably no more than 900 watts to play it safe.