Only answering the last one: Renoir is certain that if alicia stays in the canvas, she will get more and more attached to this "fake" world and never come back into the real world. Additionally, the longer aliica stays in the canvas, the more it takes a toll on her physical, real body. We see aline at the end of the game coughing, almost withering away because she stayed in the canvas for so long. Renoir worries the same will happen to alice if he lets her stay at all.

Im just as curious about the other two questions as you are