It’s not going increase or decrease with what is connected to the mixer
or what processing is active.
I guess in theory the more mics with phantom power turned on would increase
the power draw ever so very very slightly as would the brightness of the screen.
Regardless what your going to be running on an inverter you do not want to figure the
inverter capacity and the load down to the last watt!!
I would want a safety cushion, in your case maybe a 400 watt inverter.
All power inverters are not created equal, some put out a pure sine wave others it more like square wave.