Thanks for the questions. Let me give this a shot: Spoilers ahead for obvious reasons.
1. Why do you die when you take the throne? Simply put, you're in the tomb of an immortal Pharaoh who has lent his power to others over time. It is something that has been around for hundreds (or more) years. I'm a HUGE fan of cosmic horror and not understanding the choices of beings more powerful than humans. Through the other paths - greedy choices tend to get you fucked over (such as choosing the gold in the treasury). The other solo choice in the Rebirth door of attempting to escape combined with accepting the amulet - gives you an ending where you become devoted to Kannok in a not so possessed way (more of a rebirth through this route). Even rejecting the amulet towards any ending will restart the cycle, as the chosen will not defy Kannok's will. Also, think of where you are at this point. You got sucked into a door and appeared in a canyon. Taking the throne would make you the King of Nothing as there is no one to rule and nothing to rule over.
2. The Amulet. This is more of a representation. The description of it paints it as a ragged rope with some sort of rock with random symbols on it and the aura of it produces visceral reactions from the MC of disgust, nausea, etc. Although, the reader "hears" Kannok's voice through the story, you may notice the MC never reacts to the voice itself or even acknowledges any sort of voice. When you go to a treasure room, what do you expect to find? Treasures, of course! So the bond with Kannok is represented by this - and in the rebirth path, I just kept inline with what you find in the treasury.
3. The Maze: Let me start off with writing a maze fucking sucks. I think the small maze I created was over 100 pages alone and its pretty short with minimal dead ends. Most of the stuff was just for flavor because it can get super boring reading you can go left or right or straight 100s of times. I initially was going to have the rebirth path blocked on the paths with your friends, but changed it to blocking the maze path because of how much effort it would take to make. 1000/10 would not reccommended ever doing it again - but I committed to it after committing the cardinal sin as penance for my transgressions. There was also going to be a variable added to cast you as lost in the maze after so many wrong turns/ dead ends, but I was way over my head and time didn't allow for me to figure that out.
Hope this helps!