The amperage will depend on the thickness of the part, the thicker the part the more amperage required. You can reduce the amperage used by two methods. You can use an argon/helium mix, the more helium in the mixture the hotter the arc will be, there by allowing you to reduce your amperage.Or you can pre-heat the part, or both depending on how thick the part is. To choose a filler metal properly you will need to know your base alloy. From there you can choose a rod. If you e-mail myself with the particulars of your job I'd be happy to make some suggestions.