If you just want 200-250whp then don't worry about building the motor. You can make that on stock d series motors with good turbo kit and good tune. I have run 15psi on a GT28R on my stock Z6 and all I did was headstuds. Scotty runs 15-16psi on a GT25R on his Y7 and it is COMPLETELY stock. He has been boosted for over 4yrs with no problems.

I don't personally like the vitara's because of the compression and even with the FJ rods it is still too low for my likings. However, they are good for the price and have shown to hold some decent power. If you can afford it then yes do forged but I have also seen forged pistons break at 300whp. It's all in how the car is tuned and how it is treated.

O and 450cc injectors will be limited to about 280-300whp. I would go ahead and get at least a 550cc inj.