As for cures, the recipe is a guide, and if it is from a good source, should show the recommended amount of cure to use, or at least be within the manufacturer's limits. It is best to follow the manufacturer's instructions when in doubt, and you should know this information prior to using the product. They usually state the upper and lower limits of concentrations to use, as well as the normal/ideal amounts (some this info is only available online or through additional sources). Best case would be accurately to weigh your meat before anything is added, then measure the cure accordingly, based on their recommendations.
Eric