Hello Mate
My 2cw..........
I think youll find many of the answers to your questions ( listed in the posts ).....
Tig is not for beginners ( Im assuming you are ) and requires a skill set above the average welder, I use Cigweld gear and run a gas mig @ .9 wire for all my repairs, a vertical up for firewall repairs using mig will not run / drip
To stop panel warp from excessive heat, tack your repair piece into place, weld a small section, let it cool and repeat
A perfect weld is really only achievable by the person holding the handpiece with good knowledge of their gear combined with their ability