I have a V400 and am confused by what your question is. Filament remaining isn’t possible unless it has the ability to track what filament roll is on the printer and assuming they all start full.
The easiest is to weigh the roll and subtract the empty weight it isn’t 100% accurate but its ok.
The web interface has both ETA and estimated time for the print.
The PEI needs to be cool to release the print easily and with no damage. Removing the flexible plate and waiting to cool is the same as commanding the printer to heat as you remove it. As you are there it makes no difference. It literally is a few moments. Personally by the time I have the flexible plate off print removed and cleaned the printer is back to temp.
You could change the end code to not turn off the heaters but it represents a hazard as if something interrupts your interface the printer will continue to heat. I would not suggest this.