With the Dedicated Server client you will be able to run your customized server.
You can run it on your PC or in a Virtual Machine you can choose from the myriad of gaming hosting sites.

Documentation for the ".tdrServer" file: 

{{
    "userName": "EU-SERVER-USER-2", \\ you can typer what you want
    "roomName": "PRIVATE-TEST-SERVER-EU-TRACKDAY", \\ this will be the name of your room you will se in game
    "trackName": "LacrMxMini", \\ here you need to put the "fileName" of the track (you can find it in the .tdr file of the track choosen) 
    "region": "eu", \\ this is the region your server will use 
    "password": "", \\ here you can put the password that will have to be used to log in (if you decide to use it)
    "maxPlayer": 25, \\ this is the max player that your server can accept
    "sessionLength":1000.0, \\ this is the session lenght in seconds
    "sessionType":2, \\ 2 is for the Trackday session, 3 is to setup the Race session (with 3 it will use "sessionLenght" as lap numbers)
    "options": {
        "timePreset": 1, \\ 1 = sunrise, 2 = noon, 3 = afternoon, 4 = sunset, 5 = night
        "bikeCategory": 15, \\ his will be the bike category allowed in your server (to find the bike category you can check in the .tdr file of the bike you choose)
        "BikeClass":"", \\ this will be the bike class allowed in your server
        "LeanLimitlHelp": true, \\ this will enable/disable lean limit help
        "LeanLateralHelp": true, \\ this will enable/disable lean lateral help
        "LeanForwardHelp": true, \\ this will enable/disable lean forward/backward help
        "GearBox": false, \\ this will enable/disable automatic gearbox
        "ForceHelmet": false, \\ this will force all the players to use the first person camera 
        "Erosion": 1, \\ 0 = no erosion, 1 = normal erosion, 2
        "Collision": 1, \\ 0 = no collision, 1 = collision enabled
        "ManualClutch": false \\ this will enable/disable manual clutch
    }
}
You can also enable the whitelist on your server, so only player you will type can join your room. here the exhample:

"whitelistID": [
      {
        "gridPosition": 1, \\ this will be the server grid position of the player
        "steamID": "STEAM_001" \\ here you need to put the STEAMID of the player
      },
      {
        "gridPosition": 2,
        "steamID": "STEAM_002"
      }
    ]