In general, a quart of marine polish will cover a 36-40 foot boat hull, depending on how heavily you apply the polish. In most cases, a light coat with a machine buffer works well. In cases where there is heavy oxidation, it may require more than one application to remove oxidation and bring back the shine.
Gelcoat or paint in very poor condition may not come back to a shine with polish or compound, in which case it will need to be sanded, then gelcoated or painted.