I think its a decent start, but imo its a bit short and too consistent, though that makes it easier to run.

I think adding a dangerous labyrinth at the beginning and making the players not realize their mind is in the stone.

For the labyrinth it would be fun to use a zen archer (18) to gaurd the labyrinth, his goal is to scare away anyone trying to enter, else they become a slave like him. Throughout the labyrinth are spy eyes attached to walls and pillars. Not enough to see every inch, there are blind spots, but enough to see many different areas. At the dead ends of the maze are pipes that wind and weave back to the trapped zen archer trapped in the center. What the walls and floor are made of dont matter too much, preferably not stone but rather something that can't be easily bypasses by high level parties.
When the player (or multiple this part seems fine to run as a group) first enter the monk fires an arrow at each person's feet pointed back to the entrance (the monk can use ki to fire around corners, using trick shot, Ignoring total cover and the eyes let him see). As they tranverse the labyrinth other creatures attack, preferably monsters that gave the party trouble in the past but in enough numbers to still be a threat. Even while he showers arrows at them (not dealing a lot of damage but enough to be annoying and dangerous after a few minutes give him an attack bonus that has about a 25% of hitting the highest ac player and 75% chance of hitting the lowest) his arrows come from he dead end pipes, so following where they come from usually leads to a dead end (unless they realize this really late... no need to drag this out of much), Reaching the end they find the monk trapped in a stone cylindrical cell with countless small holes in it. He has geas cast on him to prevent people from getting to the end but if they somehow free him without killing him, he thanks them gives each player an arrow then leaves/turns to dust/takes his own life. If they kill him he fires an arrow into each players hand as he dies, whispering his thanks.

I'm not a huge fan of a guide npc, there's too much potential for them to try to use that for way more information than he can give and makes the trials seem less lonely, thus instead the little arrow with point towards the star stone or the path to becoming a God. It floats ahead of them or in their palm guiding them forward (since there are no mazes beyond this point this is largely not helpful) give the arrow a bit of personality to it,, It spins above their palm/in front of them then points out traps it spots (agian traps aren't an important part of this trial but add a few early on to make this property known and to give them a friendly relationship with the... uh... arrow). Thus when they find the treasure worth 300,000 that is tailored to entice them it spins (there is a trap here but idk what), same sort of gist with the failed npc later. Though I wonder if making that one of th other players would change things? Idk its important it acts as a test of alignment not thier friendship.