cson VS bip39

I prefer JSON over YAML because I spend more time confused and burned by the problems caused by it.

I understand that people don't like directly use JSON because it's not very friendly: no comments, no multi-line string, etc.

A great alternative IMHO is cson[0]. It's like JSON to JavaScript but for CoffeeScript (though nobody talks about it nowadays). It has indentation-based syntax, comments, and multiline string which usually don't need to escape. The advantage is it's close enough to JSON which is the canonical format that everybody can agree on nowadays. For YAML and TOML there are too many visual part-aways from JSON.

Or just create a JSON variant that enables comments and the backtick multiline string from JavaScript.

[0] https://github.com/bevry/cson

If you are going to take this route, I'd recommend using Shamir Secret Sharing to split your key into shares, of which you can choose some number required to reconstruct the original key (like 3 shares, any 2 can recover the key). Keep the shares in disparate locations, maybe one on your encrypted usb, one in a safe, one in a bank lockbox, one with a trusted person...

This is not good. By finding just 1 share a potential attacker has reduced the time needed to crack your phrase thorough brute force 96 sexdecillion times. Check out this amazing video about the Shamir Secret Sharing scheme which allows secrets to be split up in such a way that no useful information is revealed until the required number of shares are put together. Personally I used this repo to generate SSS shares.