First thing would be the exhaust, unless you only slightly increase the boost.

What did you base this decision on?

Here's what to keep in mind when choosing tuning parts.

Exhaust: internal diameter, smallest internal diameter part in exhaust, gas quantity and flow needed for what you intend to run to determine correct internal diameter, weight of exhaust system.

Boost controller: how fast does it control the boost? What type of selenoid does it come with? How can the boost be adjusted (according to what? Speed? rpms? gears? throttle position? etc.)

What gain could a SAMCO Hose kit possibly achieve?? Can your tuner / supplier / manufacturer prove that gain by an independant test?

BOVs: recirculating or athmospheric? AFM or MAP sensor? HKS SSQV?? Why do HKS sell an idle stabilizer for that kit?

 

There isnt really a point in recirculating the air. However, the MAF taking the recirculated amount of air into account, you should get an ECU that will accept a MAP sensor. That type of sensor will measure the Manifold Absolute Pressure (connect it to the intake manifold) rather than the amount of air going by the air filter.

There arent many places that can mandrel bend very big diameter metal pipes in the whole world. But what do we care? We just want the exhaust, right? And you can import that from Japan

Usually, big manufacturers such as HKS or APEX'i have 2 exhaust models per car available, sometimes more. HKS for example have the Hyper Muffler, the Hyper Muffler 25th anniversary edition (stainless steel as opposed to stainless back box only) and the Super Dragger; APEX'i have the Hayabusa and the N1. But there are lots of manufacturers exhausts: Creative Sports, Blitz, SARD, Trust, Kakimoto, Bullet, FGK, Ralliart, etc. And there is no doubt to me that the US manufacturers will start making exhausts for Evos asap.