My Arduino uno having : Input Voltage (recommended) 7-12V
-> I will use a resistor here to forward it 8 V to Arduino
If that means what I think that it means, that is a bad idea. You can't use a resistor to regulate the power supply voltage. The voltage that the resistor drops will vary with the current through it. Look up Ohm's law.
I want the recommended range of current for Arduino UNO R3.
There is no recommended current range for an Uno other than you must use a supply that is capable of supplying the current necessary for the circuit at the correct voltage. If supplied with the proper voltage the circuit will pull the current that it needs.