Are these 8-frame or 10-frame? As you are in VA, I am assuming they are Langstroth hives?
Traditional supers or Flow supers? Super depth (if traditional) is medium or deep?
When all of the existing boxes meet the "golden rules". They are:
- All frames have fully drawn comb across the whole frame, and
- Each frame is 80% full of food or brood, and
- Every frame is completely covered with bees.
When all of those are true, you have enough bees to defend and use the new space.
What ever your local beekeeping club says. That can vary from 40 to 80lb, depending on climate and bee strain. In southern California, my Italian bees can easily eat 40lb. In a colder climate it may be 80 to 120lb. Russians eat less. Mutts are unpredictable.
I would allow at least 2 deeps to overwinter them, then if the hives start to feel light in late fall, consider feeding.