Unfortunately, they did not leave you many exemptions. If the loan is to be secured by a 1-4 family dwelling then the appraisal rules apply. The only clarification you'll find is in a footnote in the commentary. If you search other thread you'll see it referred to as Footnote 79.
79 With respect to the example raised by a creditor and two national creditor associations – three four-unit buildings operated as a 12-unit apartment complex, the text of the rule makes clear that a four-unit residential building would be a dwelling, but a 12-unit apartment complex is not. Thus a transaction secured by a four-unit residential building would be covered by the rule, but a transaction secured by the entire 12-unit apartment complex would not be.
....Similarly, the definition of “dwelling” refers to the example of an “individual condominium or cooperative unit,” but not to a cooperative building as a whole, even though such a building may contain several individual units.
1- you'll have to look to the footnote to determine if the apartments are 1-4 family; percent of usage (compared to retail space) would not matter
2- See footnote, one unit- Yes, whole building- No