my cents of views.
piston definetly need to change. I've seen GZE piston B16A ever hit 400hp mark. But i worry more on conrod. have u compare the 4G93T conrod with your 4G93 n/a conrod? Significant different?
Downpipe need bigger. 2.5" will be bottleneck. Turbo confirm need to change.
fueling side, if i were you, i wun go for additional injector. it wun be precise and with 400hp mark, i doubt you wanna take the risk. Already most of us know majority of the stock inlet manifold, will not able to cater equal air to each cylinder and you think of this, having extra fuel spray at TB level, you will have some cylinder run rich and some run lean.
Its not Unichip cant control the main injector, its not able to control well with such a large cc of injector. That is the problem with piggyback whn you need to control any injector 50% bigger thn the stock unit. There is always limitation on what piggyback can do.
With sufficient money to throw in, anything is possible. oh yeah, i always take 15% as drivetrain lost calcualtion for manual