Garry's Mod was first released on the Valve content delivery service, Steam on November 29th 2006. It was originally a modification to Half-Life 2, but is now a standalone game.
Garry's Mod is only for Valve-released games, so no.
Buy Garry's mod 10 off of steam.
technically yes, there were a few updates it is still called Garrys mod 10 though
Garry's Mod 10
no because garrys mod requires that you have a game that uses the source engine
Garry's Mod has now updated and includes all features of 13 Beta
Garry's mod tornado
Steam
yes
You Do Not Get Garrys Mod Serials, You Buy it Off Of Steam Which can be found at steampowered.com its usually about 21 United States Dollars
There is, 10$ Steam
no