first the HKS mani is the wrong flange for a T3T4 turbo. pick up a inline pro mani and down pipe and save the hassle.

BOV will work fine and they are pretty cheap

as for a FMU on low boost about 5 psi that is BS. on stock injectors it is good to about 7psi or so, but I ran a cartech adjustable FMU for over 2 years with dsm 450's, afc, missing link, and 255lph pump and ran 12-14psi daily and 17psi at the track with no issues. I pulled the motor apart a few months ago and everything was still perfect with 92k miles on it and a stock ITR block. I also ran a inline pro head gasket to lower compression about 1 point(3mm thick HG)

I would just pick up a spearco core FMIC and save the hassle.

since it is winter take your time and make sure you at least have a front mount. DSM side mounts are junk on very low boost.

good luck and PM me if you have any questions on my old set up.

ps- a stand alone is the way to go but the set up I ran works well and has pushed stock block cars into very low 11's. I went to a hondata with 880cc injectors and 3 bar map now.