The old observatory where the Heroes of Light are based has some documents and Heroes from the Guild who should be willing to help. It should be possible to get most of the game summary from there without infomodding, aside from details that are character-specifics and the like (for more information regarding the Heroes of Light's open guild, you can check here).

Regarding Dancer-moves, it depends on said move. Waltz targets a single enemy for example whilst Nameless Dance affects all enemies. Regarding Custom Dances, it's up to the player's preference when making the skill.