Building a Dev Box

I am creating a dev box on a separate server. For testing and redundancy if anything should go wrong on my main server. Anyways I was wondering how I go about this concerning licensing? I only have 1 main site license and I do have a multi-site also but that appears to be just for running multiple websites on the same server.

Is there a temp/dev license I can use? If not can I run EE using the same key on different servers as long as one isn’t publicly accessible? Thanks!