Justniv:
3. just out of curiosity, insted of putting a resistor in every led, can't i put "high" resistor at the emmiter of each NPN? i mean between GND and Collector&Base "junction".
No, you can't. Ten LEDs draw ten times the current of one LED but if you put 10 LEDs in parallel and feed them ten times the current there is no way to make them share the current equally. Some devices will hog the current, overheat, and die.