I wonder what he uses for seed storage/backup.
Just imagine him (or anyone of us, for that matter) losing the master wallet seed.

I would think they have more than one address/wallet.
Simple opsec.
say 40,000 in each address/wallet
Yes. But even losing 40,000 coins would be devastating. I'm sure they have the proper security measures in place. The amounts they're playing with are just insane.
Being your own bank is no easy task...
[...as above...]
he once said they use an institutional custodian
Really? I would think this would be against his principles ("not your keys, not your coins" and all...), but with such amounts to deal with, I can (kind of) understand him.