Hi. 100% would be of course completing main quest + all side quest. The problem is that, looking at the game and all its features, the possibilities for a 100% run are numerous. The idea would be :

• Main quest
• All side quests
• Filling the bestiary
• Getting all achievements
• Discovering all Krak pot's recipes

This has to be segmented since it would take 100+ hours if not hundreds.