Exactly enough to be able to GM/play in the setting and improvise details consistently.
Races: Appearance, usual motivations (that is, their role in the setting or as player characters), abilities
Of the list above, only motivations should take significant space. Appearance is easily communicated by comparisons, as are abilities.
Classes: Not among my favourite design choices.
Regions: What can PCs do there? If PC action happens on political level, politics matter. If on a "band of mercenaries"-level, just tell where and what kinds of jobs they can get. General description like "mountainous with lots of caverns and underground cities" may take a sentence or three. Planes are simply a special case of regions.
Threats: What creates pressure in the setting and forces player characters or NPCs to act RIGHT NOW? Tell enough to build a game of arbitrary length around them.
Conflicts: Who are involved, what do they want, what can they do, and why might PCs be involved? Again, enough to build a game around the conflicts.
Races: Appearance, usual motivations (that is, their role in the setting or as player characters), abilities
Of the list above, only motivations should take significant space. Appearance is easily communicated by comparisons, as are abilities.
Classes: Not among my favourite design choices.
Regions: What can PCs do there? If PC action happens on political level, politics matter. If on a "band of mercenaries"-level, just tell where and what kinds of jobs they can get. General description like "mountainous with lots of caverns and underground cities" may take a sentence or three. Planes are simply a special case of regions.
Threats: What creates pressure in the setting and forces player characters or NPCs to act RIGHT NOW? Tell enough to build a game of arbitrary length around them.
Conflicts: Who are involved, what do they want, what can they do, and why might PCs be involved? Again, enough to build a game around the conflicts.