Why would anybody work?
Basically because they need an income in the Pokémon world like we do. Also, so they can afford things to buy like items and such. Or, to be like Team Rocket, work...get money...buy mechanical robots...try to catch Pikachu...fail xD
if you had the chance to go off and become a pokémon master, why would somebody chose work?
I guess, as you are young you have that natural energy to go out and try to become a Pokémon Master, but as you get older your body becomes weaker or tiresome, so you choose something more stable and not so strenuous. I mean traveling around different regions really isn't as easy as it seems.
how does an economy exist in the world of pokémon?
An economy? I guess like here in reality they work, pay the bills, help the government gain money, and so on...They probably just don't mention it.
where does money come from?
I've heard money doesn't come from trees, but it really does...seeing as it's made from paper, and paper comes from trees. No, get money like how we do, except again, it just isn't told much about...or barely at all.
do people just get jobs once they get old and then become weekend warriors?
I guess so xD
is there any sort of government?
Seeing as there are police, and all, I would believe they do have a government.