OneNote Backups and chaching

We currently have a situation where OneNote files are getting quite large and some of the devices only have limited storage (tablets etc). 

Currently I have someone with 50GB of OneNote files stored locally and its getting to the point where it is posing a problem. I want her to have full use of OneNote deskptop app 2016. 

a) Is there a way to clear the cache? Is there a danger in doing so?

b) Does OneNote automatically remove backups when you close notebooks? 

c) If you uncheck "Back up notebooks stored on Sharepoint" does that have an impact on OneNote Class Notebooks?

d) Is there any other suggestions for reducing the local data size for OneNote?

Thanks in advance for any help