[fysiks]

1. HLDS is the Half-Life Dedicated Server which is the server that runs independent of your client game and allows players to connect. HLTV is Half-Life TV which is used to allow many people to view the activity on a server without each person needing to connect to the game server. This allows you to have many people viewing the game while only using a single slot in the actual game server regardless of how many people connect to HLTV. You can also use it to create comprehensive demos (demos that have everybody's data instead of just the data available to a normal player when they record a demo locally).
2. Yes, you can use the +runscript option of SteamCMD for whatever you want. See the SteamCMD Documentation regarding automation of SteamCMD. However, you should be aware that there is a bug in SteamCMD when downloading/updating a HLDS game. The bug is documented in the Downloading an App section of the SteamCMD documentation.
3. app_update is an option that you provide to SteamCMD to tell it to update and validate an app. This is documented in the SteamCMD documentation.
4. app_set_config is an option that you provide to SteamCMD to configure it to download HLDS with a particular game (Counter Strike 1.6, Day of Defeat, Team Fortress Classic, etc.). See the SteamCMD documentation for more information on how to use it.