Best y pipe - Motordyne xyz, hands down 
  
Best intake - Injen long tube from actual dyno and tuning shops graphs/reviews or 06 airbox with panel filter (ive got HKS) 
  
Best exhaust - negligible but most likely something along the lines of Motordyne TDX or Amuse R1 titanium 
  
Best plenum spacer - Motordyne 5/16 
  
Best decats - Motordyne ART pipes, again hands down. 
  
Best cams - most likely Tomei drop in ones for n/a dont require timing adjustment. 
  
Best remap for n/a - Uprev, pretty much all you can do albeit to great effect. 
  
Best exhaust manifolds - DC Sports from dyno sheets/tuning shop experience, or Tomei and Crawford they are stainless not ceramic coated like the DC option.