Hello, 

I wanted to comment since a lot of what you are speaking about is up the alley of what we deal with in our environment.  Since you used the word VPN I thought it best to mention that Sage is not supported over a traditionally VPN and I can attest that your DB can become corrupt if tried.  What most people do is to implement it in a Citrix or RDP/Terminal Services setup.  You can in theory have the VPN running on top of that but I would recommend using an SSL based front end instead to keep overhead down.   For just remote access for a single user you could even think about something like Teamviewer if just one person needs it at a time that is remote.

Hardware wise, a box with SSD drives and lots of ram will be blazing fast for all the items you mentioned.  You would need proper licensing in place is using Terminal Services re: Windows Service licensing.  I think the larger consideration is backup or Disaster recovery and how you plan to cover that since you will be in charge of it when in house.

Excellent advice. Thank you. I have a backup and disaster recovery plan in mind I will implement (local NAS and Amazon S3). I also would run a virtual machine on the server so I can move a backup of the server image anywhere else in case of a hardware situation.

My users would be accessing Sage on the server via RDP connection. I totally understand about possible DB corruption over a traditional data serving connection.

Sounds good.  Sounds like you have it well under control. When you said VPN I was worried but sounds like you are way ahead of the game so you did not need my advice!  We run everything you are talking about on a Windows 2012R2 Virtual server on non SSD disks and it runs fine.  Even the SQL replicator.   We have a cluster setup but are running a lot more than just the Sage stuff.   We use HP servers but HP, Dell, etc...not sure that matters outside of preference.