Welcome to the Eagler's Nest and homebuilt aircraft. Skip the MIG for puddle control. Everything happens so fast in MIG, the puddle is not the same as gas or TIG, especially on thin steel. MIG is good for tacking stuff together, but gas or TIG is best for the finished welds. If you learn puddle control with gas, you can convert to TIG easily, but TIG was not around when chromoly tubing was first used in aircraft. Gas was the way to go. Since you will be learning to weld as you go, I suggest you build the empennage before the fuselage. That will give you a lot of welding practice on simpler joints. By the time you get the empennage welded, you should be competent enough to do a good job on the fuselage.
