The big question here is Tuned length manifold, so expect to pay the usual $1000 and up, only worth while from the gt30r and up range if you are after that special figure, Standard Log is fine for below that its been proven many times over Although other reputable brands do aid in gaining a better figure, but say that word reputable with good reason, as Above that low mount which has extensive mod to make it fit must have been similar design to an ebay special, and have to say that the low mount designs Do Not actually give much if any results as the hardness to get tuned length room and etc ask 6boost or other guys they may confim that for you.
For your above mods best to upgrade turbo back theres a start fmic another Cams another CAI and with the Highflow you shouldnt need to change either manifolds as both standard items will still give you excellent driveability on there own accord so theres some savings there, then again you can have dif suspension brakes to work on if you would like but unless you are planing on say going gt35r or gt3040 then highmount design external gate is the way to go then maybe change plenum and tb to suit, but at the stage you are at and highflows flowing dependant on what dyno between 240-270 all read different the standard items are fine as is spend money elsewhere.
Plus Added note change in ex manifold will most liklely result in change of turbo dump and front pipe positions as well as lines etc etc.
Hope that helps