Q: iCloud Photo Library and camera roll question

If I turn on iCloud Photo Library on my Mac and on my iPhone, will all of the existing photos in the iPhone's camera roll and Photo Stream appear in my Mac's All Photos?

And, will the existing camera roll photos be downloaded to my Mac if I have download originals enabled on my Mac?

The reason I ask is my Mac's Photos is my master library of photos that I want to keep. I might take ten photos with my iPhone of a scene, but only copy one of those ten photos to my Mac's Photos and I'll leave all ten pictures in the iPhone's camera roll. I'm concerned that when I turn on iCloud Photo Library on my iPhone, I'll pollute my Mac's Photos with photos I don't want to keep.

With that in mind, would you recommend that I empty my iPhone's camera roll and Photo Stream before I enable iCloud Photo Library on my iPhone?

Thank you!