Dropbox Help Center
Shared Folders
Dropbox Help Center – Shared Folders - https://www.dropbox.com/help/19
Is there a limit to the number of files that can be in a shared folder?
Creating a shared folder from a folder that already contains a very large number of files will often result in an error. This error only affects the creation of a shared folder and won't affect future invitations to the folder.
The simple workaround is to create and share a new empty folder in your Dropbox and then move all of the files from the existing folder into the new shared folder.
Naming Shared Folders
Make sure you pick a good name for the shared folder as the name of a shared folder can't be changed once it is created (you can change it locally but new and existing members will see the original name).
Selective Sync – https://www.dropbox.com/en/help/175
Allows you to select only the folders you want to be synced to your computer.
Copy FIles - Copy folder do not drag and drop the file out of Dropbox. Files move instead of copy when they are dragged and dropped into your Dropbox.