Brandyn
With welding any aluminum the biggest part is to get it clean without contamination. Use a fresh grinding wheel that hasn't been used on steel, or S.STL.
For repair work GTAW, (TIG) welding is probally the easiest method of welding aluminum. although SMAW (stick) and GMAW (mig) may also be used.
(the following pertains to GTAW welding Alum)
The amperage will depend on the thickness of the part, the thicker the part the more amperage required.
Two common methods to reduce the amperage are changing the gas to an argon/helium mix, the more helium in the mixture the hotter the arc will be, or preheating 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 post more information with the particulars of your job be happy to make some suggestions.