To safely secured my personal data like mnemonic phrase, login username and password, 2fa secret code, I always created a google docs. And i compressed it through winrar with a strong password and saved to my usd flash drive. Thats how i safely secured my personal data. I hope it will help you Sir.
Your method is very safe. I applied your method to accounts on all exchanges that I frequently use. Sure the hacker will never be able to hack into my account