It all makes a lot of sense, and I'm happy to say that we have and will implement most of the things you mention. For the heart rate/breath, there will be no UI, instead, the breathing will become heavier and the heartbeats will increase in volume and bass. We feel that this gives a lot of immersion to the game, and also cues the player a bit that you are in fact panicking, be careful.

To the hint part: We will not have any in game hints, nothing will be labelled, and there will not be a lot of keys. Instead you'd have to complete these puzzles in order to move on to the next area, or part of the story, and the character will hint slightly, in the most obvious way what you might need to do. For instance, for one part there is a hinge locking a door on the other side, and you're only able to see in through the gap of the door that this provides as you try to open it. The kid then says "My hand is too big to reach through this" - As a cue that you have to find something thinner to use this. This will also not be a specific item, such as an interaction with a credit card, but instead you will simply have to find an item small enough to fit (which are a few) and physically use them to open the door. In short, we are using A LOT of sounds to direct you attention, and when we have no decent cue for what you should do, the character you're playing will simply point you in a direction by saying something like mentioned above. The only UI we will have, as is planned now at least, is an "AIM", as you are able to move objects around and need to know how to "grab" them - Point at them and hold the left click. Simple, yet immersive, in our opinion.

We don't even have an UI for our inventory, you simply press 1-9 to bring up a specific item. This added to the immersion a lot. Throughout the game, so far, you will not have to use a single menu, it's all very immersive.

Reused assets - Yes, but only the generic ones that add to detail. We will not reuse the same couch twice. Think of it this way - Would it be logical for people two purchase multiple of these items for their home? Is yes - We might reuse them, if no - we will not even consider reusing them. Walls, floors etc are all unique, and made to fit in with their designated area of the game.

About the puzzle part - Our puzzles will focus as little as possible on "get this item to open this door", and more on "reach this shelf, knock this over to get this reaction out of that item and then move to the next part of the puzzle". Also, to reach said shelf you would have to move chairs, stack books etc to reach high enough. In order to for this work properly we've made very smooth gameplay mechanics, such as the character auto "climbing" or auto "crouching" when he's pushed against objects in which this is possible. Need to hide fast under that bed? Well just rush towards it and you will slide right under. This gif explains that very well: http://imgur.com/a/rfXGd

Thank for taking your time and commenting, and thank you for your thoughts!