Hi,
Nice idea...
For this operation to get performed in a sequenced a manner you will need to centralized all the functions using a microcontroller... the choice will be yours be yours based on your previous knowledge about microcontrollers... i prefer PIC conrollers and a C compiler MikroC...
You can use thermal sensors like LM35 connected to the controller with ADC subroutine helps to measure temperature and put a threshold value (max temp) above which fire extinguisher has to work... for sensing temperature from multiple site use multiple sensors....
For the fire extinguisher to work use electromechanical valves which operates on applied voltage.....
thanks