I'm not 100% sure what guidelines you're referring to. In general terms, the biggest thing you need to do correctly is to use space types and define the "Standards" information for these (Standards Building Type and Standards Space Type). It'll make your life easier if you use the library files that ship with openstudio as starting points for your space types (eg: get the MidriseApartment space types for Corridor, apartment, the Large Office spaces types for Open and Closed Office, Mechanical Rooms, Stairwells, etc), that way you're sure the residential versus non residential will be taken of correctly, and the loads (LPD, etc) will be affected correctly too. Aside from that, you obviously need to specify the Proposed building HVAC system because that's going to be used for the fuel determination in the baseline.

To answer your second question, yes, the measure will take care of mixed use (Residential/non residential) as well as mixed fuel, should they pass the threshold from ASHRAE 90.1 Appendix G. It will also take care of the exceptions for Internal Loads etc.

The logic for 90.1-2010 is best described from PNNL-25130, especially section "3.1.1.2 Process for Determining the Baseline System". The Logic for other vintages of 90.1 is similar but adapted. (2007 is basically the same, 2013 is way more complex... also handles the primary/secondary daylighting zones and controls)

As far as I know, the only big thing that is currently not implemented anywhere in openstudio-standards, is the baseline fan pressure drop adjustment, because there's nowhere to define if you have MERV filters etc in the proposed model and the logic can get awfully complicated anyways. This you will need to do manually...

I guess I should've been more clearer on this. By guideline I meant by some tags that we need to provide (for ex, "fenestration type" tags to the windows construction etc) & luckily my long-term memory worked to figure out this later.

Thanks for the answer too.