Don't worry, take your time! I'm not going anywhere I'll go ahead and address some of your points.
1. I'm glad you like Rebecca! Other than a few furthers hints I'll drop near the end of the story, most of the clues are already there for you to turn over. The question isn't so much what made Rebecca snap, rather, it's why was it enough to make her snap. A question I'll explore more with her daughter in coming arcs.
2. Unfortunately, you're not going to get much more Jessica/Rebecca interaction. An unfortunate side-effect of the story's placement in the timeline. Hopefully her next, true rival will be even better...
3. Funny you mentioned that, I'm actually in the process of re-working Blackburn's map as we speak. It's in an interesting city, with inspiration from a dozen cities and some unique elements all of its own. All you've really seen so far is parts of a quarter of the city
4. Unfortunately, I feel inconsistent dialogue quality is a con of having multiple writers, but I will do my best to take that advice.
5. I do my best to make POV shifts smooth, but some shifts are unavoidable. Any tips on how to make those shifts less confusing?
6. I usually aim for around ten pages a chapter, but sometimes it comes up short or flows over.