KJW M700 Takedown Upgrade Questions

Okay everyone, so I recently got my hands on a KJW M700 takedown and am looking for some upgrade advice. Firstly I will be HPA tapping it, which brings me to my first question, Im looking for 2.3j with .32g bbs at 90psi (aka 500 fps with .2's). That's the psi I run my Daytona gun at, and im wanting to run them simultaneously off the same regulator.
So my question is what is the shortest barrel length would allow me to do this (Im planning on using a 6.03 or 6.05)

Also if I do shorten the barrel will I be able to use one of these:
Steel CNC 14mm Negative Adapter for M700 Series Airsoft Sniper Rifles, Accessories & Parts, External Parts, Adapters - Evike.com Airsoft Superstore

And last one for now, are the stock KJW valve knockers made out of steel?