How to correctly setup the salt for the crypt remote?

[ncw (Nick Craig-Wood)]

it seems that one must provide the same pair of password and salt to successfully encrypt and then decrypt a file via the crypt remote.

Does that mean a salt is effectively another password that the user must memorize/write it down in case the rclone config may be corrupted or lost?

Yes that is correct.

You don’t have to use a salt, but it is recommended.

Furthermore, I am wondering what is the difference in the safety aspect between a) providing a really long password (say, 256 bit or 32 ASCII characters) and b) providing a not-so-long password + a not-so-long salt (say, 128 bits for each).

The salt is all about stopping dictionary attacks on your password. So a 256 bit password would be more secure than 128 password + 128 bit salt.