Yes - at least for Multiplayer. Goto your Call of Duty 4 installation folder and rename the subfolder 'miles' to 'dismiles'. That is it!

Yes and no. It depends on the server's settings and game mode. Obviously it would make no sense to have FF on in a Deathmatch game (Free for all). Some serves run FF in either one of the Team Game Modes (TDM, Headquarter, Sabotage, Domination, Search and Destroy). Infractions are punished differently as well. Some servers suspend you for a certain amount of time (no kick - just respawn delay) others kill you immediately, but you will respawn as usual.

If you die by FF it will usually not account for stats.

Hardcore refers to the level of difficulty. In Regular Mode you have a HUD which provides infomation about your weapons and ammunition, a cross-hair, granade and explosive warnings and lots of health. None of that is granted in Hardcore Mode - it is as real as it can get! No little helpers, no second chance when hit. You might survive a hit in your limbs and recover, but that is about it. Anything else will end the life of your current spawn.

Servers running on Hardcore usually carry that or an "HC" in the name.