Help.

[Ram48]

I am a hobbyist welder and am looking for a Tig. I want to learn the skill and will do mostly motor-sports type welding (when I get good enough) usually no more then 1/4 to 3/8 thickness both steel and aluminum. My question is what size machine will fit my needs and if I had to do 1/2 inch what size would handle that in multiple passes? I am looking at 200, 225 and 250 Amp inverter type single phase 220 welders.
Thanks
Ray Mc