Switched from Aperture ... missing photos

I just finally switched from Aperture to Photos ... not because I wanted to, but because I feared a sudden incompatibility that would strand my photos forever. It was a process because my library is over 200 GB, and was about 80% referenced, 20% managed. So first I moved everything over to the external drive, including the library, consolidated it all so that it was all managed, and then let my computer run overnight to create the Photos library. When I woke up, it was so far, so good, except that:

1. The photos library has about 56 fewer photos/videos than the Aperture one did? Is there any way to track that down?

2. Photos.app has crashed twice already.

3. I use My Photo Stream, but not iCloud Photos. I think it is clear, that, like Aperture, it imports the Photo Stream photos and doesn't just delete them as Photo Stream fills up -- is that right? But the other issue is that it doesn't seem to import the photos instantly like Aperture did, and I'm not sure why. Does it only do it when you first open the app?

Thanks all!