As to what deduction is attributable to a qualified trade or business as well as our view on Prop. vs. Final Regs, you may like to refer to this discussion: https://proconnect.intuit.com/community/Discussions-Tax-Reform/Proposed-vs-Final-Regulations/td-p/10...

There is not much science in how the adjustments are made.  If an expense is attributabe to multiple qualified trades or businesses, it'd be allocated on a prorata basis (e.g. 1/2 SE tax deduction).  If an expense is specifically attributable to one single qualified trade or business, it'd reduce the QBI ony for that particular trade or business.

It's not clear why #5 is relevant for QBI adjustment.  QBI has already been reduced by the bonus depreciation.  #4 and #5 also do not reduce the UBIA, which is used to compute the applicable limitations.