Just an update to my specific situation.
Client had a volunteer who builds sound proofing walls for hospitals help with the construction of the wall. He discussed some of the same things I suggested (y'all suggested).
Double wall wasn't used. Not sure of the double Sheetrock either (they are using the fireproof stuff so I assume denser?) anyways, not sure how it turned out as I was leaving before the wall was done.
Thanks for the suggestions! Good info here, great as a reference for future endeavors.