I can build this solution using Node.js.
On client side, if the file size is very huge, I can split them up and then upload them on server.
As most of the time is involved in IO/Network operations, Nodejs would be a good fit, IMO.
Are you okay using MongoDB on the server side?
How large can be the files - (200MB, 500MB , 1GB or even more)?
Will you be able to show me how you deploy your code to Digital Ocean or give me access to your Digital Ocean account to deploy code and test them?
Also, what is the server configuration that you have opted for?