The docs for the API are available here: http://skynations.net/modapi/annotated.html
At the moment you can add IGameServices which can run constant and update within the server. See TestService.cs in GameData/Scripts. You can also edit commands via Chat.cs. You open the entire project file with Visual Studio at Scripts.csproj in the same directory. If you check out the existing stuff in Chat.cs it's pretty simple to learn from the pre-existing commands in that. Do not hit compile however, the server will compile the scripts when you start it, hitting compile in VS will do nothing. It will stop and show errors during the compilation if it finds any.