Hi,
Id do something like this..
a good spread of big and small
Size (oz) # Qty Total Oz
100 2 200
50 5 250
32 15 480 (32oz is 1kg)
10 19 190
5 10 50
1 30 30
Total: 1200 Oz
The trade offs to consider are
big bars will generally fit into a smaller area in a vault, and spot will be cheaper.
Bars over 100 oz may be harder to sell, unless its back to the dealer for spot.
1kg and 10 oz seem to be the sweet spot in terms of buy/sell spread. (IMO - please correct me if I'm wrong here)
You still want some silver in small sizes in case you want to sell a small amount at some point in time.
Cast or mint - doesn't matter