when the steam release happens I think the subscriber should have priority in the queue
people that have a verified account second free to play they will have to wait behind everyone else
if the server gets overloaded and I don't think releasing a second server would ever be a good idea what I recommend doing is using the funds you earn to soup up one server it's capacity to the Limit and never rent servers from other people you should always own your servers
if you can make everybody spawn in one area it's possible for you to pick the spawning location for people when things get too populated what I recommend doing is expanding the world and adding more Hardware and move the spawning location to that area and still have the 6 month server plan I think two servers won't be a bad idea but at the beginning I think there should be one server like you're planning just upgrade it then later use the money you saved up in that time to make another world and server with similar capacity