The maximum amount of current flowing through your ESC will be determined by the motor and prop selected for your plane. Your battery and ESC capacity should be rated to handle this amount of current without overheating.

The wattmeter is a very useful tool that will allow you to measure the amount of power that is being delivered to the motor/prop as you advance the throttle. This information will tell you if you are overtaxing any of the components of your power system. As a general rule of thumb, none of the components of the power train (battery, ESC, motor/prop) should be become very warm (too hot to touch) while delivering an excellent power level (approaching 1:1) to the propeller.

Some digital voltmeters may serve in place of a wattmeter if they can measure high current levels of up to 30 amps. Many meters can be effectively extended by using a current shunt and measuring the voltage drop across it under load.

There are many excellent stickies describing the essentials of electric power systems. Once you are familiar with just a few key concepts, you will have no trouble selecting the right components for any power level. The brushless/lipo combination is a very effective power system.