IW5M Game leads to a magnet URL. Use any torrent client, such as Utorrent and Bitorrent for example.
All DLC files lead to a direct download link.
Open the .iw5dlc file to install "requires the latest version" of IW5M.
To open the .iw5dlc files you must first run "LaunchIW5M.exe", once you do that it should automatically choose the IW5M folder click yes and it will begin installing the DLC# to your IW5M folder.
Face off maps and Terminal are included already when you download the game.
If you are receiving an error where you can't play one of the DLC maps, or you can't play IW5M without an error.
You may need to remove caches.xml from the game directory to update your latest DLC or get IW5M to work properly again.
One last thing to note, Single Player is not supported by IW5M, however there is a zip file provided with the game torrent, to allow Single Player to work.