Dont change too much at one time - gets confusing - change one piece at a time - tune and learn what each change does
the TPC goes into the bolt - its the adjuster basically - the stock one has a covered face and vents on the sides with a flathead notch on the top for the adjuster to turn it - if you get a different TPC you will change your tool a bit (usually take off the end cap)
When tuning for shot count - you will possibly need a spring kit or assorted springs (main and back) to change your pressures (tho some regs are adjustable - never used a reg on my phantom so /shrug)
not sure whats local to you for parts - I usually get mine from CCI directly but I am stateside heh
1) always check your pump handle lock nut - make sure it is properly adjusted (not eating your body) and that it is secure to the pump handle so it does not turn (nor allow the pump handle to turn) as that will change the stroke and may cause big problems.
2) when tuning for shot count be aware that you might lose a bit of consistency on the very ragged edge of shot count - so adjust and learn.
3) whenever tuning - using the same paint with good bore match and a good chrony are important - variance in the paint, barrel match can cause you to tune WRONG lol
4) barrel length matters if you are using CO2 - the shorty barrel will get less fps per shot - best lengths are 11in and 8in - 6in shorty no bueno.
5) use good co2 - MOSA/Lelands are great and consistent
6) time, temp, pressure, humidity are all factors to some degree - not much but a tad
honestly imho I am happy over 30 and will change as the situation demands. but to each their own =)