I was going to type up a large post to share what I think about what I've gathered from your post, but I realized all my answers boil down to two questions to consider:
- How different are your apps from each other? If they're really different, you probably want different projects. If they're mostly the same with minor UI cosmetic changes, then you could probably benefit from a shared automation project structure.
- What does your team want to do?
These are all questions that you and your team are best able to answer.