As Genghis has said, you'll still need a CPL. Since you'll probably be working in Europe, an Instrument rating will be a must.
Therefore, you may as well do the ATPL theory too. (Covers CPL, ATPL and IR theory). The best news is that you can do all of this modular.
Pick the school, find out their contacts and connections.
Aerial Application - aka crop dusting - is very specialist work. I don't know any one who does it here - maybe someone does? I have a mate who does it in Australia (and Canada). Definitely need tailwheel time for that.
What do you mean by Air Courier? Charter work? Bizjet work? Again, contacts are essential. So's experience.