I can try to answer some of your questions:
●MJH plan: that was all enacted in the first 3episodes. His plan was to get Mei Lin to kill him and then the case will be reopened. He had the whole conversation of his plan with his right hand man in ep2, its on minute 47:44 on kisskh. What we ended up watching after episode 3 was a new plan since Mei Lin had proof it was not him, since she figured it out with that fake plate, which lead them to find all the other players. So the bulk of the story is not the original plan they already did it, just ML did not kill him.
●Master of Shadow/MJH: I don't think it would have fit in with this new script he used a bit of it, when he killed that fake guard and was acting out loving Mei Lin over the top lol...
●LM:I think this was a case of bad acting by the actress and directing. I could see the script probably wanted us to see her falling in love from when she went into the room dedicated to her. I mean even when she was supposedly in love with MJH, her expressions of love to MJH were more just demands like "go fight your brother, win this hunt and I am going to put your name on this paper you will marry me", her expressions were still just cold. With the CP arc since she was not doing the chasing she couldn't just use words, she has to act out falling in love, she still just remained cold. She has had the same expression for most of the drama. She was able to use words with CP to show her change in heart when she said "I would have chosen you" . I think the script had actually done a good thing in placing this arc when MJH, had disappeared. It just wasn’t acted out well. It was a good placement of that story, as she would then be open to someone else and know what it's like to be loved, than her chasing someone who didn't care. I am actually starting to think she probably wasn't in love with MJH just maybe more like puppy love, as she did say to CP he should have confessed earlier.
●CP: Agree he should have had a terrible death, a The Double type of death, both main leads being the one to do it lol...
●Emperor: Typical Emperor, we are lucky in any drama to get a good one, they are hard to come by. Especially we now know he knew MJH was framed. He just wanted to keep the so called "peace" and have answers for his subjects quickly.
●YQ: Your comment is funny, lol.. Hostage Princes usually don't get to do much unless they have a great advisor, I have noticed in some c-dramas. They are busy trying to not rock the boat too much and stay alive. They have enemies at home and hostage place.
●Princess Zi Gu: Not much to say here it goes with the time period, but do not care to see it lol...
I think it will be a HE, hopefully lol.....fingers crossed.