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12 or 24 are both fine.
As why choose one over the other, 12 is easier to remember, but may be “harder”^(*) to import into Ledger or Coldcard in the exact same way that 24 words are “hard” ^(*) to import into Trezor-T
The reason there is “no real difference” between them is the same reason why using a 12 word seed is “no different” than using a 240 word seed (if such a thing existed). More is only better up unto a point, after that your just spinning your wheels.
As for passphrase, I use sd-protect, so don’t need them, but find them useful for account labeling and isolation. Passphrase “car” for my new-car savings. Passphrase “xmas” for my Christmas savings. Stuff like that.
^(* what some call hard, others may call simple)