Can I delete photos off Camera Roll after transferring to iCloud?
Deleting photos from the Camera Roll has no effect on photos already in your PhotoStream and vice-versa.

Photo Stream is temporary so if you don't access your PhotoStream on your computer where the photos can be saved locally on your computer (there is an option to do this automatically with iPhoto on a Mac), you should import the phtoos from the Camera Roll with your computer. You can delete the photos from the Camera Roll after the photos have been imported by your computer as with any other digital camera.