It depends on a few things... If you're going to do those things by using only a single device, it'll only give you a false sense of security ^{[it heavily depends on how secure that device is]}.

Yes, you can also extend your seed phrase on Unstoppable:
^{Note: It's not recommended to import your seed phrase from one wallet into another one (regardless of whether it's supported or not).}

Create a new wallet > Advanced > enable Passphrase option > Type your passphrase and confirm.