This seems pretty nice, I wouldn't attach it to the globals file though but rather make separate one. It might not be a bad idea for job functions to return dictionary. I would suggest an alternative mode to only show if something increases or reduces income without clean percentage.
Agreed. All you really want to know is "what is the best job for this person, all things considered".
The exact amount of gold and XP should probably be shown as a description - similar to what you have for the slave "inspect" screen. All that's important is that different jobs describe the same amount of gold/XP in the same way.
The way this works right now is fine for my personal use (and it was quick enough to build). But if you'd like to put it in the game, I can rewrite the job functions and integrate things better. Hit me up at 8nbp31+3qz9yqhm7yrws@grr.la and we'll get in touch :)