To the OP: Welding specialty aluminum alloys is challenging for a beginner. Frankly, it is easier to weld titanium and get good results than to weld thin-walled aluminum—just a fyi. The natural progression, in terms of complexity and skill level, is: lug brazing, fillet brazing, steel TIG welding, titanium TIG welding, stainless TIG welding, and aluminum TIG welding.

I am questioning your decision to start with the most challenging.