been awhile since posting here, but I need help from people that know the EJ20K motor in a Version IV STi Wagon with 50,000 kilometers on it.

Car was bone stock except for an exhaust until last month, I had the following work done:

Timing belt
tensioners
timing guide replaced
NKG-R plugs and new wires
Greddy Profec B Spec II Boost controller added
FMIC installed (used item)
Blitz BOV (atmospheric) (also used item)
HKS intake
Apexi Power FC (also used item)

above 3000 rpm's the car is fine and pulls strong. Below 2500rpms it likes to hunt a bit at idle and then stall. Also when at a stop light when you try to accelerate (under normal load) the car also likes to hesitate, sputter and often stall.

my tuner wants to run a VG30DETT MAF, Fuel regulator, Upgraded fuel pump and injectors...

I am really hesitant to do this, because of the car not having issues above 3000rpms.

from the internet the following seems likely:

MAF going bad
IACV going bad
O2 Sensor going bad
Vacuum leak

One thing I did find was that the atmospheric BOV was not set and was leaking badly at idle, closed it down and car was fine for about 30 minutes. Definitely going to replace that with a recirculating BOV.

Can you think of anything else I should look at that might be causing these problems?

Only one Tuner in the area and I really don't trust him at this point anymore.

Appreciate any help. I am currently out to sea and just trying to narrow down what I will need to look at.

Thanks in advance for any ideas.