You will have to source a stock solenoid for your boost, Im sure someone on here will let you borrow one. As for SAFC, you have to take it out. Strut braces are fine. I had them front and rear, not a problem. Wouldnt know about the engine dampener. As for the diff. I had an aftermarket one in there too. They didn't drive my car anywhere so don't worry bout it.
Trust me people make it seem like getting an EPA or Defect as the end of the world but its not.