Mate if you only want what, 280-300rwkw, you could basically do that on a stock bottom end.
Realistically pistons are a bit of insurance, but at the end of the day detonation is detonation, and it will kill your motor either way.
Especially considering you cannot tune.
The oil pump dying issue is blown massively out of proportion here unfortunately. Yes some have failed, but out of the 1,000's installed every year, without full disclosure (things like limiter bashing & tune related) then its even less again.
Highly unlikely you'd bust a pump if you have half a brain and dont drive the car balls on 8,000rpm everywhere.
Honestly if it was me?
Just have a factory rebuild done.
Install steel wheeled factory turbos and simply be happy with 250rwkw on a factory ECU which will at least give you some known reliabilty.
That is the most cost effective solution for you, without and added risk or failures which i can see will occur in the future unfortunately.