The only limitation is how much is in the hot wallets at the time. That's usually a minimum of 50 BTC when they will get topped up with another 100 BTC. If it's more than that then they just have to wait for wetsuit to top it up which will be done within 24hrs.
To find the biggest one you'll have to do some blockchain analysis on our 2 hot wallets. 3LaNNTg87XjTtXAqs55WV5DyWASEZizCXZ and 329koRvovTyNnd4ADrpR2uJHzXxfvKxta5
Holy shit that is some big hotwallet, I would say without much hesitation the biggest of ANY site I know, and I think I know or play at almost all of them right now (bitcoin and crypto only, not those fiat with crypto integrations ones).
I mean, even 5 BTC hot wallets are hard enough to find, let alone a MIN of 50!