Since using a few (say 4) of them and connecting them directly to the output pins would draw too much current, obviously, I need to use a separate power source to power the leds and three transistors or MOSFETs (not quite sure about this as well).
But since I am planning to make this a standalone device I would like to know what the best way is to power this device as a whole (Arduino + LEDs):
Two seperate wall warts (one for Arduino, one for the LEDs)?
Just one wall wart?
What about the different LED forward voltages?
The effect the series resistor you use. However equal currents does not equal equal brightness so you will have to play about to get the white balance correct.
Power it like this:-
Wall wart (9V preferably)
LEDs from the +5V line of the arduino (through the resistor) to the collector of the transistor.
Do you have common anode or common cathode LEDS, that link didn't work.
I was wondering: since I'm not quite sure how much (read: enough) current the 5V pin can deliver due to the voltage regulator, wouldn't it be a better idea to use a 5V regulated ac/dc adapter, to power both the arduino and LEDs?
As they have 2 common cathodes each, you can't run them in series. I'd use three BC327 (pnp) transistors, emitters to +5v, collectors driving the appropriate colour LEDs (each one with its own series resistor), base to an Arduino PWM pin through about 470 ohms.
Total current draw from +5v with all LEDs on will be 4 * (30 + 30 + 30 + 25) = 460mA, plus the current taken by the Arduino itself. The Arduino regulator can probably just about handle this with 9v input, although 7.5v would be better. If using 9v, feed it through the barrel jack so that the protection diode takes some of the power dissipation.