I'd skip hardener until you are ready to paint something for real, and make sure you have the appropriate full face respirator or fresh air supply when you do use hardener.
Rust-Oleum enamel thinned with naptha will be fine for practice. Air pressure depends on the gun. If I were you, I'd sell those antiques and get a $16 HVLP gun from Harbor Freight, and learn how to paint with that. It is easier to clean and will not be as much of a loss if you fail to clean it properly. I have painted with both a cheap HF gun, an old one like in your picture, and a very expensive HVLP gun. The Harbor Freight one will do 90% of the job of the expensive gun in an average users hands, with a bit more over spray. That old gun will have tons of over spray, and if the seal on the cup isn't perfect, you will be dripping paint everywhere. Ergonomics are also terrible.