1) That depends on your definition of complicated. I'm assuming you mean difficulty. If that's the case, by all means, make it a challenge. People that play this should feel like they earned than win if they beat it, right? Just make it in a way where there isn't just one path to winning and isn't so hard that it becomes frustrating. It helps if the difficulty is directly tied towards the overall goal you want the players to aim towards. Honestly, I'm one of the ones that have no clue what Prom Story, so it'll be interesting to see how it plays out.
2) Ask yourself this: Do you want to remake Wolf Spirit? If so, do you want to, because you feel obligated towards it or because you really want to expand it. Are you willing to put the time and effort to follow through with it? Can you? Is it fine as it is despite being linear? Consider your answers before going through with it.
Only you can answer if you should remake Wolf Spirit. However, a part of me wants to tell you no, because not only do you not know what branches to add, you don't seem as enthusiastic about it as the other two. On the other hand, I never had the chance to play Wolf Spirit, so that might be a factor.
3) It sounds interesting. The premise is good, but I wonder how the execution is going to be. From the look of things, the story might be linear for a while until the player wakes up from the hypnosis, which is rather fitting in a way. I don't mind it, but I hope the payoff is good.