The current drawn depends on what devices and circuits are connected to the Arduino.
If your Arduino runs successfully off USB then the power draw must be less than 500 mA (1/2 Amp) so any 7 to 12V supply of 500 mA or more should work.
How much of maximum total current ( from all I/O pins including 5v pin) can be drawn from the arduino so it doesn't fry?
according to Ohm's law input resistance of arduino is greater than 10 Ohm. Right?
If you use a 7V supply (2V drop) you can draw 1A.