>>715997772
there's not much lore to get, it's just gensokyo is a place where youkai exist. 90% of the lore is just knowing what tengu or kappa are and that there's a shrine maiden whose job is stopping youkai who cause problems.
if you really want to learn more about the setting, then reading perfect memento in strict sense and bohemian archive in japanese red are the lore dumps you're after.
i'd also say read some manga. three fairies manga, forbidden scrollery, and wild and horned hermit are my recommendations.