Is there a way to make Photostream take up less space on an iPad without turning it off entirely?
a) figure out how much space Photostream is occupying on the device


Go to settings
General -> Usage
wait until the top is done and then click on Photos and Camera
The next page under Photo and Camera has the space used for Camera Roll, Photo Library, and the Photo Stream.


b) reduce space.

After taking photos you can edit and crop, delete the ones that you do not want.  It saves the last 1000 photos for 30 days so if you take a lot of photos, copy them when you can.  Photo stream is there for you to easily sync your photos from one device to all.  After you have the photo, copy it to your mac and remove them from your photo stream.  After 30 days or over 1000 photos you might start to lose photos.