/diy/ - Do It Yourself

Rate my design please.

I'm planning to build a modular coil gun. At the end I want to be able to chain as many coil modules as I want to increase its power.
I'm also using the JP headers in place for the MOSFETs that I haven't decided on yet.

Main module:
While off, the gun discharges the capacitors through an 1M resistor. For that, I added the PNP transistor that is controlled by the 5V power supply. Once that one is off, it discharges the caps, otherwise not.
While on, the gun uses a simple charge pump to charge up the capacitors. To ensure safe charging, the ATTINY85 reads the voltage and stops charging once ~95% capacity is reached.
Pin 6 produces a PWM signal for the charge pump in place of an oscillator.
Once charged, the READY signal is on, indicated by one or more LEDs. When the trigger is pressed, it sends the FIRE signal for a second.

Question: Is it fine if I just build my own coil for the charge pump? If so, how many coils should I use here?