The routes aren't really that hard to 100% tbh, except for klaus that is a secret route, there's a score method to track what route you're in, but it's not visible in the game, still the only thing you really need is just pick any choice that is related to the characters you want, please note even if you pick a specific route there still will be situations where you interact with other characters and that's normal
Also about Klaus there are a lot of ways to get to his route, I did it by starting asking Devon about the key at the start of the day (he will then give you his jacket, you need it) then go to the forest after asking to the janitor, then follow Klaus in the forest and play that part, you still need to continue on Devon route afterward but don't wait for him when he put the telescopes back indoor, and then follow Klaus into the forest, and that's all :D