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The microcontroller provides a reliable/stable current/voltage control than a simple resistor, and also provides more possibilities such as: pattern flashers, and transmission of data. Led's connected to microcontrollers can also be used as testing equipment.
You may need more than 2ohms but 3 watts should be sufficient, although I would personally prefer slightly larger, like say, 5 watt. (I look at it this way: better to be safe than sorry.)
It is extremely possible, 2400mA x 2= 4800mA. Given the low consumtion of led lights, that should be sufficient power for more than 36 to 48 hours of continuous output.
LEDs for Beginners