E-braille settings

Hi All, 
We are getting our ereaders at long last, and I am doing the behind-the-scenes work. 

How many cartridges do you allow per patron in Duplication for ebraille ? I am looking for a good default setting, just like we have for the audio. NLS suggested and calculated 5 per patron for audio, but I am told the ebraille cartridges, they can download them right away and send the cartridge back. And since the files are so small, we can send a lot at a time.

I was thinking cartridge limit 3, and titles on cartridge limit 15. What do you think?

Thank you for any tips you can share as well.
Have a great day! Maureen