You should be looking at transimpedance amplifiers, not discrete circuits with switching transistors.
You need to ensure you protect against high voltages blowing up your amplifier.
APDs are run close to breakdown. While for experimentation purposes you can set the voltage manually, a full design requires some means of adjusting to compensate for the high temperature coefficient of the breakdown voltage.
Make sure you limit the current from your high voltage power supply to the APD to a level that the APD can withstand. That only needs to be a resistor.
Keith