I am no longer in poultry, however, the internal audit we did took me 2 full days each and every month (1 QA manager, 1 HACCP coordinator and 4 techs)
It was split into areas of the plant (facility included cut up as well as slaughter) and then broken down into it's parts (doors, floor, ceilings, chemicals, evis machines, chilling etc etc etc)
Your operational inspection IS NOT a replacement for the monthly IA, it should include things like GMPs proper handwashing, hairnets, gloves aprons etc
The monthly IA looks deeper.......traffic flow, colour use by department (we had 4 different PPE colours depending on what part of the plant), close inspection of maintenance SHOP.......where are the knives sharpened?? Is it sanitary? Screens on air intakes, chemical storage locked, dosatrons working,
So start by walking thorugh the plant and REALLY looking at the BUILDING.........this is your best chance to catch nonconformities before USDA inspectors do
Oh and walk ins (cooler and freezer) .......when were they defrosted last etc
Labels on products in the walk ins.......clear/correct
Dry storage----clean, covered
Hope that gives you a good place to start