1) 3,000 cfm is the OA threshold at the system level 2) System mapping should not change based on DCV requirements. Also, it's unlikely you'll only have one zone of a multi-zone system requiring DCV as (90.1-2016) G3.1.1-C probably requires a dedicated system. 3) Doesn't matter. The zone total OA just has to match the total cfm specified in the design (or as allowed by 62.1)