OK first: Plagiarism itself is bad style but it is actually not illegal in itself. As you say plagiarism is trying to pass of somebody else's work as your own, so the concern here is primarily about fame and only to a lesser extent about money. So if you make clear that you are quoting from P and P you should be fine. I would consider putting all passages that are direct quotes in italics to mark them, then it should be obvious.
Violating usage rights is much more serious as you can be sued. Unfortunatley fair use is a legal defense, not a free ticket (which makes this really massively unfair). Fortunately the usage right for P and P have long expired. So that's likely not a problem here.
Honestly my main worry I would have with a project like this is that my writing would end up next to Austen, which could turn out not to be a favorable comparison.