(Unfortunately, we are only able to answer one question per posting. Other questions must be submitted separately.)
In terms of the narrator's point of view, we learn several things throughout the story regarding his feelings about the experiments and the scientific advancement they represent. Some are inferred in his observations, while others he confronts openly.
When the narrator's colleague, Baglioni, discusses Rappaccini's brilliance with his lack of concern for human life, warning the narrator against Rappaccini, the narrator is not put off. When he gets a sense of evil eminating from the garden, the narrator overlooks the feeling. Even when the narrator sees two creatures die—the lizard and the insect—he does not embrace these observations with serious concern.
Warnings the narrator has felt alter in the presence of Rappaccini's daughter; they change and no longer concern him: he is not sure if it is because he has forgotten his concerns or because of feelings of passion he may have for her. In all these ways, he is struggling with Rappaccini's advancement of science.
The narrator continues to be aware of what is happening to and around him, but ignores the threat: when Beatrice had grabbed his hand before touching the purple flowers, she left the mark of her hand on his, though he attributes it to some insect that has stung him. When he cannot stay away, at one point he says, "He hastened into that Eden of poisonous flowers."
As his relationship continues with Beatrice, as limited as it is (for they cannot touch hands or kiss), his suspicions visit him "like so many demons."
After another visit from Baglioni and his pronouncements of doom (when the narrator is given an "antidote" for Beatrice), he wonders if Baglioni's observation about a strange flower-like scent in his room might, in fact, be coming from him, so he breathes twice on a spider and it dies.
Joining Beatrice's company once more, the doubts which have assailed him take root in his heart, and he accuses her of plotting to poison him. Realizing what her father has done, she is devastated. And because she has taken the antidote so that she might be with the narrator without fear of his death, she dies: that which took the live of others has given her life; without the poison within, she dies.