Man, if it werent for practice... I'm not a natural and I have to keep doin it. Hard part for me, and the thing I try to work on most, is welding LOOOOONG consistent beads. I'm building a tank right now that is 44' in circumference, roughly 14' diameter. They dont like starts and stops cuz its potentially a point where the tank can leak. The tanks are most commonly x-rayed, and the one I'm on was also vacuum tested.
On part of it, before I put it on rollers layin down, I had the bottom part (only 4' tall) standing and had to weld walking around it. I was welding about 11' at a time while walking.
Stainless to carbon isnt hard to do as long as the scale is grinded off the carbon real good, and the filler wire wether MIG or TIG is stainless. I love TIG welding! Difficult for me to figure out how to use both hands...
The knowing part with different materials and processes just comes with doin it over and over again. Its a competition for me. I look at who is the best and figure theres no reason I cant do it, so I set out to, to be among the best. Anything else is complacency, mediocrity, or laziness.