There's something not good in is info: t in between the bov and intake vaccum hose, not shure but you cant plug the wastegate on there, it has to be on the piping from the turbo to the throttle body.
my friend built one for his turbo gsr and he said it spiked like a mofo. i have no experiance or anything, i just showed him the site and he said that was his personal experiance, just letting u guys know
Yes, mbc's can only increase allowable boost. If you want to lower boost, get a wastegate with a softer spring.
You can get rid of the hose on the turbo by connecting the mbc directly to the wastegate, and the other end of the mbc running to a T between the bov and the intake.