i found that with mods the twin turbo system is not the best
i had a prova ecu and to be honest its not really worth the $$$
get some downpipes and a system i had a full rage system and it made the car alot more responsive and have more power if you end up with an overboost or spike you can drill out the little pill in the primary boost line before the tee
a turbo upgrade to vf26 on primary and vf27 or 32 secondary is the best set up you can run
also a ZS controller could be a good idea to get rid of the vod
and you can get different intercooler to suit but mostly the top mount you have is probably good enough for the power you will make with twin turbo you can get ARC ones sometimes on trademe
i had mine running rage pipes heatwrapped prova ecu and 18 psi and it went really well but it wont last forever
another option is go single turbo that way it opens you up to a much more driveable set up and you can keep modding as much as you like if you ran a vf22 and sti ecu would be alot faster than the twin set up