Best Practice for Assigning Items to Default Subinventory

We are on Oracle R12.2.5 and need to set up and identify default sub-inventories for a specific business sector for picking.  Long term, we want to do paperless picking.  This is not a WMS enabled organization and uses picking rules and SO release rules.  We are trying to not pull from the MMT table due to the size of that transactional table.  The purpose of this is to identify which building pick/pack/ships from which building location based on the item scanned.  We are not using MSA, either.

We have sub-inventories A, B, C....these are all in different physical locations with only specific pickers assigned.  We want to assign specific items to each sub-inventory as a 'default', but allowing that item to be in other locations also.  We do not want to assign the sub-inventory at the item attribute level.  We will be using/setting up Min/Max planning for this business down the road.  These items will already be moved to WIP sub-inventory if used for assembly on discrete jobs.