Dont bother! get a MIG welder. I used to struggle with an arc welder for allsorts, they are perfectly useable for some jobs if your good at welding, however to be good you need to be doing it every day.
IMO Mig is far easier to use, neater weld and more versatile. I Have a 160 amp sealey one which was cheap and OK for most stuff up to around 5-6mm thick when used with 0.6mm wire. You must use argoshield or cougarshield gas though CO2 is a total waste of time, the weld goes in cold and lumpy with poor penetration.
you can even weld some cast irons with a mig, and you can get brazing wire too, also stainless and aluminium with pure argon.
I dont think i have used my arc welder in the last 5 years!
You can get high pressure disposable argoshield cylinders now too which last a hell of a lot longer than the small low pressure disposable ones you used to get.
Best option is a hookey full size cylinder with no rental if you can get one of a geezer, the big L size will last me literally 10 years!