This is how I installed S4MOD...
1) I created a separate installation for FPSC (on a second hard-drive) which I updated to v1.07
2) I renamed
FPSC-Game.exe to
FPSC-Game_original.exe
3) I put the S4MOD executable into the folder where the original FPSC-Game.exe was....
Now when you run FPSC and test game and build a game it will use the S4MOD executable...
To answer your questions: Yes it has Airmod and as long as you are using Iron Sight compatible guns then yes you will have them automatically in game...
EDIT
Curse my incredibly slow typing speed
"Quoting yourself is stupid and self-centered"-Thraxas