Go for MIG welding, it's the best welding technique for welding autobody panels. This also means taking your time focusing on the steps that lead up to the weld itself. Sizing your patch is an essential skill. It may add some time in the beginning, but it will save you hours of cleanup and patching later. Remove ½ to ¾ of an inch of good, clean metal around the area you intend to patch. Keep corners rounded to prevent heat buildup which will cause distortion. Check your metal gauge. When it comes time to cut, precision is key (This is where that pneumatic saw is useful!). A flush weld is going to look and hold better than a lap weld. Measure twice, cut once!
Some useful links:
http://weldingrage.com/