martys, a few things. On your PCB, make sure you wire up the RS232 com ports so that you can connect the PIC to a PC, with a little PC software, monitor plot and log your spectrum decoder + other variables during debugging. Also, add a ceramic beeper or speaker to one or 2 of the PWM outputs so your lamp controller can make acknowledgement sounds.
The next step is how are your math programming skills?
Are you expecting to use someone-elses code, or, are you going to process the raw ADC yourself?
How are you powering this thing?
Note that even in ultra low power sleep, powering the electric MIC actually consumes more power than a sleeping MCU will use.
Having enabled at least 1 of the PIC's op-amps, 1 comparator and an internal voltage reference to have the MCU awake on a degree of noise thresh-hold will raise the power consumption from the high nA range to the mid uA range. Doing some careful data sheet reading and tests, you may not want to use the deep sleep or comparator, just run the MCU at 32khz with ADC running at tight loop around 1khz waiting for the beginning of a spoken word, then jumping to high speed xx mips mode to process, then back to slow mode. In any event, I would expect this method to consume power in the 100-50uA range. (not good for 2xAAA batteries power supply, but fine for 2xC or 2xD batteries) Your gonna need to decide how much power is appropriate VS code and responsiveness. Powering up and down the MIC opamp and MIC itself might introduce effects you will need to work out. External ultra-low power op-amps exist which may run at lower power than the ones in the PIC, but, then have very low bandwidths.