Add Multiplayer To Existing Game

I and my community would like to have designed a multiplayer game for Microsoft Train Simulator. The idea is the same as like what has been done for GTA San Andreas which now has multiplayer and the site is [login to view URL] when the application is open the user selects a server and then the game loads. There is currently a server app for those who wish to host multiplayer and a app for those who wish to play the game. I wish this to be the same for Train Simulator. So, Id like a app that integrates with Train Simulator in a way to where players can see each other in an open world. Wed also like trains to be dispatched and what I mean by this is a person can load a track profile and control a trains path and set switches for the players and control movement on the route. This can be all-in-one application or separate applications to do each thing I described (multiplayer, server, dispatch) but at a bare minimum we'd like a environment to where each player is able to see each other. I believe this can be done. MSTS had whats called "explorer mode" this is where a player is in a open world environment with no time constraints and if this could be taken advantage of, then hopefully a person could host MSTS on there server and run continuous operation until the server is restarted and then all trains would reset to there default environment when the app was first loaded on the server. These are just ideas and Im up for suggestions but I wanted to give an idea of what I would expect. I would like to say Im not asking anyone to break copyright law and the software would have to be created to where the user would have to have Train Simulator installed before they could play multiplayer. Im willing to pay a good sum to whoever can provide results. Thanks.