If you are cleared to descend to an altitude then I would have thought that the clearance automatically permits you to temporarily level off at any altitude from top of descent to cleared lower altitude. Presumably by the time the first notch of flap is needed the aircraft would have been at 250 knots reducing, and nearing 3000 ft agl. The most efficient deceleration is level flight idle thrust. Selecting VS to 500 fpm merely delays speed bleed back.