Hi,
I have a great deal of experience working on decentralized systems. I have done a similar project quite recently for another client and can complete this one pretty quickly.
I have several questions regarding your file sharing app,
Does it need an ability to stream (music or videos)
Should it have a link sharing ability (this will complicate things a bit, but still possible)
Android IOS?
You mentioned that it should work with a file server, do you mean an ftp, should we consider any other protocols?
Hope we will work together!