The tutorial ends on day 2 and doesn't include Thaddeus (except through unnamed mentions), but it has to be followed in the order it happens. After the game takes off the training wheels on day 2, you can do anything you like in whatever order you like. Will everything be equally effective or useful? No. Do I punish the player for making the "wrong" choices? No. Feel free to play the game however you like.* Is it necessary to play this game like a visual novel and strictly follow the tutorial (because I hate the idea of leaving Thaddeus touch Evelyn)?
It was never designed with the mindset that someone might want to stay faithful to only one girl, but I am probably going to expand earlier scenes at some point to accommodate this kind of playstyle. It could lead to negative consequences during the endgame, though.
Right now, probably not. Scenes such as the one early on with Belle are unavoidable for now.* Is there any way to get the MC's first experience with Evelyn?
I almost always give the player the chance to try again if I block off scenes in that way. You don't have to play this game in a way where you feel you have to be at a certain level of ability training by day X. You're not even supposed to be able to pass all those tests. Specialize however you like.* If I miss a scene because it is not yet possible to reach the necessary skills to see it will be able to repeat in the future (such as training with Nell) or would be better if I wait a few more months to play and the game is more complete?