Ditch Nitrogen and go CO2. They both provide the same output at the same pressure. Nitrogen is only advantageous when you want pressures of 1000+PSI, otherwise, you get less Nitrogen shots compared to CO2.

I did a few density calcs and youve got over 45kg in armour/chassis. You might want to remove that urethane from the front and just beef the hardox up to 6mm.