It depends on whether you are using Photos or not. The app’s features are different because it leverages the Photo library when possible.
1) R+J is supported as a pair when using the photo library. In the file browser, they are separate images. Photos stacks the images together; there is a menu item to switch (as Aperture had). You can batch switch as well in Photos. That feature is not present in RAW Power because Apple has not provided a way for me to do that.
2) My library is under 2TB, so everything fits in the cloud.