Red/Green/Blue - approximate values from experience. Read your device's datasheet.
Higher will only make the LEDs dimmer and not damage anything.
Total current - your supply may be capable of 5V, and a gazillion mA- the circuit will only draw what is needed, limited by internal resistances, or LED current limit resistors.
Look at the top right - X1 is barrel connector, D1 is reverse polarity protection diode, U1 is the onboard regulator.
The voltage before the diode should be ~7.5V, the voltage after the diode ~6.5V, and the regulator will output 5V.
Connect your RGB LED anodes to Vin.
Make sure your walwart is >=7.5V (up to abiout 12V). You don't need the external diode, but it does offer extra protection.