What would the requirements for 100% be?

Sorry for the late reply, but we've determined the requirements for 100%.

• Complete all 82 Quests (75 main quests and 7 Cotton quests)
• Complete all 17 Challenge quests
• 100% Collection / 145 entries in Library (55 creatures, 12 plants, 19 ingredients, 23 dishes, 36 treasures)

Beating Time Attack quests are not required.

edit June 27, 2019: 100% category is now on the leaderboards.

Just a heads up, since Curly was updated into the game in v1.0.2 along with 7 new quests, 100% and All Quests requires you to do all 89 quests. (75 main quests, 7 Cotton quests, 7 Curly quests)