There is no set dimension for the slack in the H16 forestay. The shrouds and jib luff wire should be tight.
Basic rule of thumb for rigging: The boom blocks should touch or nearly touch the traveler blocks when fully sheeted for the days sailing conditions.
The jib luff wire and shrouds should be tight. Adjust the shrouds down, tension the jib halyard / rig and check the sheeting. Repeat if needed.
Flying a hull will depend on wind strength, sailing angle to the wind and weight on the boat.