Probably a good thing on an rb30det if you can get a big exhaust housing, but i wouldnt be putting one on an rb20. Remember its essentially a 380rwkw turbo with a cropped exhaust wheel, so it will be lag city.
I would just refit the timing belt correctly, then do a comp test. The easiest way to undo the crank bolt is to put a breaker bar on the crank bolt and crank the motor. Or stick it in 4th with the handbrake on tight.
Is your cefiro a twin cam? Im assuming it is, so you will have dramas with almost everthing ecu wise, as the rb30e uses a dissy. Why nnot just buy a second hand rb25 for $800 and rebuild that?
I wouldn't use stainless, as it reacts with aluminium. There is no reason to not use aluminium, m/s or brass. I would just get some alloy tube, or you can buy hollow locating dowels (like head dowels).
IMO if the stock 70mm thick intercooler is fine for 350rwkw, then a 100mm one should be fine for 450rwkw. How much power and boost are you looking at running.
Probably the biggest you can get. Even big turbo cams are small when run on a n/a. Probably 280's with 11mm lift, however you will have to spend a bit on the valvetrain. Personally i would keep the vct.