Not necessarily. You need a game using Source SDK.
No you need the full game or any other source engine
Not specifically. You need a VALVE game to play Garry's Mod, one of which could be Half-Life 2.
Yes, you do. You need steam and a source game such as Counter-Strike: Source. Or Half-life Source. Day of Defeat Source
In order for Garry's Mod to work you need a minimum of one Source Engine game eg. Half-Life 2, Team Fortress 2 or Portal.
Only for the half life 2 version of garry's mod.
For Garry's Mod to work, you need to have downloaded at least one Source® game. This could be Half-Life 2, Counter-Strike:Source, or Team Fortress 2.
No you cannot because Counter Strike 1.6 runs on the original counter strike engine. Every game on garrysmod must run from the Source Engine or any game ran off of HL2. From my memory, These are the requirments. You must have ONE for gmod to work. Garrys Mod*Required Half Life 2 *You need this for basically everything in Garrys mod Half Life 2 Episode One Half Life 2 Episode Two Counter Strike Source Team Fortress 2 Half Life Source Day of Defeat Source
Not necessarily. If you own absolutely no Source games at all, then you can buy it, and you can then run Garry's Mod. A lot of Garry's Mod addons require Counter-Strike Source though, so it's recommended, not required.
Yes you need half-life
no, but you do need a source game like Half Life, Half Life2, or Team Fortress2
Yes you do. Counterstrike: Condition Zero, however, is not a mod of Half Life, and therefore, does not need Half Life to acquire.
No, but you need .lua to make your own addons.