I am bit confused about the power requirement of Nano. It stated that unregulated power supply should be between 6-20V and regulated should be at 5 V but at what Amp
The current capability of the power supply should exceed the current requirement of the circuit. The Nano and the attached circuit will draw the current that they need. If the circuit needs 500mA it does no harm to use a 10A power supply as long as the voltage is in specification.
Suggest you do not use the "Vin" for the internal regulator at all. It cannot supply useful amounts of current.
Just use a well-regulated 5 V supply - such as a "phone charger" with a USB outlet - connected to the USB connector (or the 5 V Vcc terminal and ground if it is a 5 V supply and just has wires). The Nano itself uses less than 100 mA so any 5 V regulated supply with a rating of more than that will work just fine.
It partially depends on how many pins are used as outputs and if it's going to be battery powered or mains. 1 pin for an LED requires less than 10 pins for LEDs.
If batteries are the source then how long you want the nano to operate is another factor.
groundFungus:
The current capability of the power supply should exceed the current requirement of the circuit. The Nano and the attached circuit will draw the current that they need. If the circuit needs 500mA it does no harm to use a 10A power supply as long as the voltage is in specification.
Unless you accidentally short the power. Then get ready for some melted metal!
Indeed, but if using really high current supplies you already have fuses to protect the wiring from catching
fire don't you? Hope so!
I'd like to say yes, so the one on the side of the house counts?