Hi looking good!
Dont believe the hype on the intakes, they dont give any increase in power whatsoever and even if they do give 5hp on a dino, you won't feel it at all. Go for the Takeda intake, it sounds great!
As for the ECU, its cracked down, no one has unlocked it so no chance of a remap.
The only way to get extra performance is through the Supercharger. I believe Aimgain do a good one for the IS250 but yes, its expensive and you won't find many (if any) second hand.
An exhaust setup may be good if you want some sound too - HKS is a good place to start.