Hi, and thanks for your comment! I'm so glad you enjoyed the game. (I'm not sure how much of a newbie you are anymore if you've completed all the routes!)
Adam's route is doable in normal mode, but there isn't anything extra you get from normal vs easy mode, so there's not really a reason to redo it.
There's a list of collectables in the behind-the-scenes book, available for a $15 donation. There's tips for some of the harder ones here, but I'd prefer to keep an outright spoiler list of them as a bit of a premium thing, since the game is otherwise free: https://itch.io/t/928910/collectibles
The sequel can be preordered now, the demo is free to play, and there's an alpha build you can get access to after preordering, but the game isn't quite finished yet: https://bobcgames.itch.io/zags