Saw on a post someone using : dedicated-server server and servers. Not sure to merge the first one with the last two, but server and servers could be synonyms. I'm not sure we needed the server tag to be distinct from dedicated server, because as far as game and servers are concerned, we will always run on dedicated server. Other type of server could use mutual-server or other tags.
Yes, server should be a synonym of servers. But dedicated-server should not, in most cases they are the same and just servers should be used but there are some question where it is requred. Any questions that involve the actual server software itself or is specific to a third machine doing the hosting will need this tag.
As for the second request I can't think of any time they wouldn't be synonyms, and installation is my personal preference out of those tags.