Answers:
1. Not sure
2. You can use you own music.FPSC supports various kinds of music files but tends to work with .ogg the best.You can download Audacity for free to convert your music files.
3. Yes.But flashlights are items you can pick up and use as objectives,keys,etc.The flashlight will not function as a flashlight although if you search the scripts forum you might find something that will simulate the use of a flashlight.
4.You make the game.It is possible to put dialog in the game.Again there is more information about that in the scripts section.
5. I believe it is in stores but I am not sure what ones.Someone else may know.
I hope this helps.
FLa
Where you can find my demo:http://www.savefile.com/files/6970524