Y27JLC

Bare in mind that this is my first high powered car, well, high for me anyway, I have a few questions that could be stupid and maybe not so.
I bought my car in January and it ran fairly quickly, then the turbo intake pipe split so I replaced it with a silicone one which was just a cheap fleabay one so sort of fell to bits.
I replaced said cheap hose with a full snorkel to turbo standard setup with pipercross panel filter as it had a cold air intake with a cheap cone filter, when replacing the turbo pipe I noticed that all of the connected pipes had all been blocked off one way or another apart from one. The recirc one was obvious as it has a hks ssqv thing or possibly a copy one. Are the smaller ones supposed to be linked to anything or do they get blanked off because its running higher than standard bhp?
There is a perrin 3 port boost solenoid which I would assume should have 3 vacuum lines coming from it, as it has only 2 im confused as to why?
The boost guage that is installed has started to show only 0.4 bar boost whereas it used to and very occasionally shows 1.2 which im guessing is max?
Today I have replaced the vacuum lines for the boost gauge and fitted the t piece to the vacuum line on the front of the throttle body, took it for a spin to see if it fixed it and coming off a roundabout to a bend in the next road the engine seemed to just cut power, have I made a mistake by linking it into that vacuum line?
The car has a list of modifications below:


Sti intercooler
Sti pink injectors
Td05 turbo
Milltek decat
Straight through custom exhaust of unknown make
Pipercross panel filter
Perrin 3 port boost solenoid
Walbro fuel pump
Unknown remap and unknown power, in the advert it said bob rawle had set it up and I have a printout fot 300bhp from 2009.


Any help would be massively appreciated as id like to get the car running better than it is if possible.