If you use the "Copy file" action on dropbox, then you only need the URL to a given dropbox item to place in the field named "Source URL" ... DropBox URLs that have dl=0 in the query (everything after the ? in a URL) will link to the page for the given file or folder, if you change that to dl=1, then it becomes a download link!
There may still be size limits that you need to deal with, but this should help you handle basic file operations.
I've been using it with G-Drive for a year now (not the DB connector) and have been most satisfied with the results. Whilst this in and of itself isn't necessarily a solution, hopefully it can help you get a bit further along with managing this.