Using Box server-to-server: will it support our app?

We are working on an ASP.NET app and our company wants to use Box to store documents and send links to our customers.  Our employees will be generating large documents (too large to send directly in emails), uploading them to Box, and then sending emails with the Box links to our customers.  We don't want to require anyone to have a Box account other than our backend application.  We will be using the Box .NET SDK, not the Box API (I think there is a difference).

Some questions:

• Can this be done using the Box .NET SDK?
• Do we need any other accounts other than the service account associated with our application?
• I'm hearing our access credentials expire -- 1 hour?  60 days?  Other than initial setup, can our app continually use the Box service without having to manually login?  If so, how?
• I recall reading a FAQ there are some bandwidth limits with Box.  If we have dozens of employees generating uploads at the same time, will our app be shut down?  Can we avoid this?
• Is there a COMPLETE end-to-end .NET application using the .NET SDK which shows how to upload a file using the service account and retrieving its shared link?  I'm only finding snippets or code using other technologies we can't use.  Or, I'm probably looking in the wrong place.

If you need additional information, please let me know.  Thanks!