#Bitcoin key security levels:

Level 0: Not your keys.

Level 1: Hot wallet (keys on online device).

Level 2: Single-sig cold wallet (keys on eternally quarantined hardware)

Level 3: Single-sig cold wallet w/ passphrase

Level 4: Multisig

Level 5: Multi-vendor multisig

Level 6: Multi-vendor multisig w/ passphrases

Level 7: Multi-vendor multisig w/ passphrases, geographically distributed

Each level increases your security against particular vulnerabilities, but complicates your setup. Find the highest level you can confidently operate.