I really enjoyed solving these puzzles. I think that the door temperatures should be somewhere visible all the time that I don't need to click the door constantly. I also thought that there was too much messages, but it was good that you didn't need to read all of it before you can continue. So I didn't really bother to read all of the messages, I liked to solve them by testing that what can I interact with.
Then some feedback on your questions
1. It had a good difficult curve, at first the levels were simple and they got bit more complex with time but not too much. So the puzzles were easy at first and at the end of the game not too hard, but not too easy either.
2. I didn't find any bugs!
3. Even if I didn't read all the messages I still figured out how all of it works.
4. Art and visuals were great! Maybe the panels could be bit better looking.