Restrictions and limitations on Onedrive Business files and folders

You can sync up to 20,000 items total across all synchronized libraries

You can sync up to 5,000 items in a SharePoint library

In SharePoint Online, file names can have up to 256 characters.

Folder names can have up to 250 characters.

Folder name and file name combinations can have up to 250 characters.

File size lime 2 GB (10 GB for consumer version)

https://support.microsoft.com/en-us/kb/2933738