user30212: If I want to power up 6 normal 3mm LED with the appropriate series limiting resistor, do I need the 5V with 1A or 5A power supply? Same goes to the Arduino, if I want to power it externally, do I go for the 1A or 5A? 

user23002: Depending on your led, it will draw 10 to 20mA for a standard led. Thats 0.010 to 0.020A. Multiply this by 6 and you see that a 1A power supply will be enough.
Your arduino, when driving those leds, will also use a few mA. So you can power everything with a 1A power supply.

30212: <p>If I want to power up 6 normal 3mm LED with the appropriate series limiting resistor, do I need the 5V with <strong>1A</strong> or <strong>5A</strong> power supply? Same goes to the Arduino, if I want to power it externally, do I go for the <strong>1A</strong> or <strong>5A</strong>? </p>
 23002: <p>Depending on your led, it will draw 10 to 20mA for a standard led. Thats 0.010 to 0.020A. Multiply this by 6 and you see that a 1A power supply will be enough.</p>

<p>Your arduino, when driving those leds, will also use a few mA. So you can power everything with a 1A power supply.</p>
