Passphrase advantages

Hi all,

I have a Coldcard on order and I’m planning on moving from an old ledger nano.

Couple of questions. I’ve done a lot of reading but just wanted to clarify a few bits before moving everything.

Passphrase - As far as I read, adding a passphrase doesn’t actually increase the entropy. But it does add another layer of security in the event my seed phrase is found by unwanted parties. (See discussion in below thread).

https://www.reddit.com/r/Bitcoin/comments/p5o3jg/does_a_passphrase_increase_the_possibilities_of/?utm_source=share&utm_medium=ios_app&utm_name=iossmf

Therefore, if I am confident in hiding my seed phrase well, as I see it, so long as that seed phrase remains hidden (off line, no cloud storage etc) then adding a passphrase increases the complexity for family to recover funds.

Therefore, potentially little benefit in my circumstance in adding one? Unless of course I want to create a separate wallet within that seed.

Exporting a watch only wallet - I am planning on setting up a watch only wallet on bluewallet. Is there a difference between me exporting an xpub and the .json file? There was a post on here a while back with a discrepancy of funds using the xpub. Is this down to the derivation path?

Finally, xpub, zpub, ypub - are these all in relation to legacy, segwit and native segwit derivation paths? If so, does that answer the above question whereby exporting the .json file will show all transactions? Where the xpub would only show certain derivation paths and not those with zpub etc?

Ta