Not a big professional in the operations like one attempted, but i think it is doable.
20 kg batch would be somewhere 2+ liters of molten metal + some dross/slag. As I imagine the whole process... I do not think you need such a big crucible, but it will be somewhat quicker with larger one=higher area for heat transfer.
As the silver melt, it will flow to the bottom and drain through the hole, so this could be done continously, just adding more raw sterling and harvesting shot in some high and big steel barrel with good water circulation.
"Heat management" with the cooling water should be considered, because cooling down 2 L of molten silver is not a joke
without steam explosions and other accidents.
Many times, crucible is perforated with teeny holes near the top. And as you grab it with tongs and tilt it, molten metal pour through tiny holes at the top to water basin, creating small grains of metal. Nice and even in shape
For this ammount on regular basis, you should maybe consider some tilting furnance.
Also think if the material of crucible could be drilled - not to develop cracks. Graphite will be OK, but with sintered materials like clay/SiC+clay etc. I will be cautious not to crack expensive stuff
and wreck the drill bit because of hardness of material
but it could be drilled tho, it is brittle and slowly goes through, but cracking is a real issue.
Good luck with project