1st: On the map where you have to get the chisel by throwing down a rock the well-like hole on the upper floor, when I go down to get the chisel, a monster spawns down at the stairs. I wait a bit and it vanishes. Is this intended? I keep thinking the monster should spawn first, then I go up, throw down the rock onto the monster to kill it and save me - and coincidentally get the chisel by doing so.

2nd: Whenever a monster spawns in a scripted scary moment (for example when you pick up the blood for mixing the explosive or that one in the long corridor right before the library) and it kills me, when I respawn the monster won't spawn anymore and I can just go on. I'm not sure what to think: On the one hand it's good, because it prevents a potentially frustrating series of trys to find the right way out of the situation. On the other hand I also would like find the way to escape that the author actually had in mind but I can't because the situation won't happen anymore. What do you guys think and prefer?

The lever "riddle" in the water-works can be tough if you slow down just a little. So when I was too slow several times in a row, this made me think that just pushing these three levers is not the solution. I thought I had to find a fourth one or something. Maybe a note with a hint that speed is important could help here.

I think you should really look at that area in the library where the player can get stuck. There are two tinderboxes there that people will want to pick up so it's likely to happen to a lot of players. If that's too much work, maybe you could create an autosave point when entering the library like in the beginning of the temple. Then people could at least reload at a close spot when they get stuck.

I had the heart/alter-problem, too. I jumped up to put the heart in that shaped place. To me, it would make more sense if this spot was the right one instead of the stand of the alter.

I've found the hammer in the water works, but as far as I understand I also need the chipper to combine it with the hammer. Is it correct? Because I cannot find chipper neither in the water works nor in the dining hall.

Use the hammer on one of the door's lock. It's pixel hunting though.

I didn't see the lock itself in the first place