Cold-Wallet Security System (Multi-Share + Passphrase)

I have designed a security architecture for my cold wallet management and would like to have it audited for potential security vulnerabilities.

I intend to use a Trezor Safe 7, utilizing the advanced security features Multi-Share (Shamir Backup: 3 shares | 2/3 threshold) and a Passphrase.

The setup is as follows:

1. I generate a 20-word seed phrase as a Single-Seed option via SLIP39.
2. I then transition from Single-Seed to Multi-Share. After this, I possess both my original Single-Seed phrase and my three shards for the Multi-Share recovery.
3. I apply a Passphrase. Whether I perform a recovery via the Single-Seed phrase or the Multi-Share variant, the passphrase is required to access the corresponding wallet.
4. I distribute the three shards at three secure locations using Trezor 'Keep Metal' devices. Inside each 'Keep Metal', I include a physical note containing the passphrase.
5. I keep the Single-Seed phrase at my home.

I see the following advantages:

1. Redundant Recovery: Multiple recovery paths via both the Single-Seed and the Multi-Share variant.
2. No Single Point of Failure (SPOF): This applies to both the seed phrase and the passphrase, as the latter is stored three times (once per shard location).
3. Protection against Social Engineering and Wrench Attacks: Since the passphrase required to move funds is not stored at home, this prevents immediate forced transfers.

Disadvantages:

• Increased Complexity and Cost: A more demanding system with higher expenses for multiple 'Keep Metal' devices.
• Error-Prone Setup: Generating the seed phrase and stamping it into metal is time-consuming and prone to mistakes (a total of 80 words must be recorded and stamped).
• OpSec Risks: Concern that the security measures are disproportionately high, potentially causing operational security errors rather than increasing actual safety.