You don't have to do the rods and crank for 425hp out of the RB25, they are plenty strong enough for that. If you want to start pushing high revs, constant 7,500+ then yes I would suggest doing the rods. The factory cranks would be more than fine for up to around 650hp. After that I am not sure.
JE forged pistons are a great upgrade and cheaper than Trust, Jun, HKS, etc. I would also change the rod bolts to ARP as the factory ones are a bit weak for constant huge power increases. A mild set of cams that suit a decent turbo that will flow that, and a front mount intercooler and you should have no worries.