All the advice you have is dead on the money. As a professional welder, I can tell you that thick metal is easier than thin. Flux wire takes a bit of getting used to, so just take your time. Clean your welds with a wire brush as you go and after a while you'll watch them lay in nice and smooth. Also, make sure the metal is nice and clean, rust or even the film of oil to keep rust from forming will give you hell. If you need any tips, just ask. I've welded everything from 1/8th to 3 inches thick and it's all fun.