You can check the recovery seed that you are creating (what you write on the paper).

Trezor's software and hardware is open source, so you can check any part of it.

There are different things you can do to prepare for different failure scenarios, though not everything is automated, it's better to test some things by hand.

1. Failure scenarios a scheme can/can't protect against

2. How to setup the system for that scenario

3. Recommendation on how often to confirm system and backups

3a. How to recover from failed hardware

4. Recommendations on lifetime of system until replacement

4a. Recommendation on recovery if system is compromised (physical theft)

Essentially where is the best practices guide?

This is the best Trezor has, it's quite limited though, but good for koderately technical user.

For storing large amount of money you can hire experts.