Could be the turbo, definitely with a loss of power but you'd get an engine light if it was. Unless there was an intermittent lack of power which could be caused if some of the blades in the turbo had broken. But this wouldnt explain the white smoke or issue with the brake pedal.
Plus one of the main causes of white exhaust smoke and coolant loss is a cracked or warped cylinder head, a cracked engine block, or head gasket failure caused by overheating. ... A cracked head may allow coolant to leak into one or more cylinders or into the combustion chamber of the engine.
what's the coolant level like?