Welcome to the FreeTrack "Crew"
Here's a couple answers.
1. The 4 LEd's obsolete because the 3 LED manages the same accuracy with less power consumption and a euro saved on the extra LED.
2. You always need to use resistance with LED's
http://www.free-track.net/english/hardware/calcled/
Use that calculator to calculate how many of which one you need
If you want, I could do it for you, but I'm going to need
a) your battery voltage
b)your LED Voltage
and
c) Your LED Forward Current
3. If Configured properly with good solid hardware(good, Wide angle LED's, a good webcam that can achieve 30 FPS without using up your processor too much
http://www.free-track.net/english/hardware/webcam.php) the Yes, it could very much achieve the same tracking quality.
The biggest problem you'll probably see is your processor being used a little more to handle the camera, TrackIR gets it done within the cam. But if your computer's fast enough, you're god to go.
4. Sorry, I have no experience with the game so can't tell you that one.
)