The main thing with ali is to just clean the the crap out of it. brakeleen and a rag until it's not oily then scrub it with a wire brush.
When welding my cast sump is get contaminants coming to the surface. I just fed in heaps of filler then ground the weld back flush and did the weld again. The first weld was always full of black shit and porosity. The second weld was always beautiful like welding clean plate.
probably won't find that in a text book but it worked for me and others said the weld would be impossible.
Also I find the small electrodes way nicer to use than the fast ones unless doing heavy stuff. I'm not sure on the science behind it.
If learning I'm not sure if a foot pedal is the best thing to start with. It might be fine or you might find that is just one too many things to think about.
The hardest thing I had to learn was self control. If you blow a hole just stop, let it cool off a little then try to continue. In bursts till its closed.
edit lol blow a hole