The best option for long-term investors is to use a hard wallet,because there will be only one wallet, so even if their devices is lost, there will not be much trouble about these passwords and seed phrases.
First send your seed phase or private keys to your emails, also use them to compose a little song only can listen anytime, write it down in your diaries, and makes sure have a google doc to save your wallet keys and other information.
As for storing password and seed in your email, I would not support that at all, because the chances of your password and seed getting into the hands of hackers are very high in email. If your email is ever hacked, understand that all your passwords and seeds will be easily known to hackers, and you will know this when the hacker will transfer all the assets from your wallet to his wallet. Online things are more accessible to hackers than offline things.
However, you can save it on a piece of paper or in your diary, this is a good practice and recommended by all wallets company.