Pretty sure ultramon will do this for you. There is a free older version around I used (since paid for it) allows you to set boot profiles for monitors so would only boot with two enabled and the 3rd can be shortcutted to switch on off.
It does work in "background" as in it sits in the system tray if that's background enough for you?
If you using ATI, then CCC allows you to put start bar on one desktop.
To turn the montiors off, you could setup profiles or you just push the power button?