Depends on the tokens. Ethereum (ERC20) tokens can all be held in the same wallet, though I wouldn't recommend it. Spread them out so there's not one point of failure. If they aren't all ERC20, then a hardware wallet if your best bet.
If somehow one of his wallets get compromised its highly likely that all the others will be also though... security measures are usually the same. If you dont want that many wallets, keep the coins you own the least amount of in an exchange i guess... would make your life easier but its also riskier!