Yeah, a hardware wallet is good, although for a billion dollars, 100 hardware wallets would be better. Could even go so far as to split a private key into seven horcruxes using Shamir's Secret Sharing and bury them in locations around the world.
Memorizing a seed phrase leaves you vulnerable to a $5 wrench attack, I wouldn't recommend it.
Memorizing a seed phrase leaves you vulnerable to a $5 wrench attack, I wouldn't recommend it.