Both Jekyll and Hyde were aware of what happened to each other and Mr Hyde was Interested in what happened to Dr Jekyll
The process of brainstorming involves making a list of ideas. You just write everything that comes to your mind, without any order, so that you can gather as many ideas as you can to write about.
What it means is that he wouldn't have been able to get where he got if it hadn't been for the scientific achievements of his predecessors. If it hadn't been for these "giants" that enabled him to see so far, he wouldn't have been able to make all the discoveries that he did. For those coming after him, he was a giant that enabled them, and so laws and theories and scientific knowledge always increases based on the knowledge before it.