there is no estimate for when Garrys Mod 11 comes out
technically yes, there were a few updates it is still called Garrys mod 10 though
Garry's Mod has now updated and includes all features of 13 Beta
Buy Garry's mod 10 off of steam.
You can get Garry's Mod 9 for free, yes. But Garry's Mod 10, (11), you have to pay for. But Garry's Mod 10 is really worth it, in my opinion.
Garry's Mod 10
no because garrys mod requires that you have a game that uses the source engine
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
E
no