There are no cheat codes in Garry's mod as it already contains a sandbox mod where you can fly around and spawn props. But I know there are some commands you can insert into the command console. Such as sm_cheats_1 which enables third person so If I were you do a little poking around to find some stuff like that.
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
E
There is, 10$ Steam
no