I thought the whole point of replace-by-fee was so that it wouldn't be classified as a double spend.

What's the collective opinion here?  Is the segwit wallet implementation "bullet-proof" and completely trustworthy for meaningful amounts of bitcoin?  Has it passed the same kind of code review process as the older wallet implementation?

(I'm aware the bech32 address format may still conceivably change, I'm just talking about the safety/reliability of the wallet, for example, being confident that the generated public and private keys always match, and you won't run into a situation where you receive money to a certain address and can't ever spend it because of some bug).

I think the answer to this is "no", but would appreciate confirmation.  Thanks.  I want to make sure the other addresses in my wallet are still secure, even after revealing the private key to one of the addresses.

Is it safe to use the same mnemonic seed that you use for your solo wallet as the seed for one part of a multisig wallet?  Is it safe to use the same mnemonic seed as a part of two different multisig wallets?

What kind of isolation is desirable when using Electrum in Tails for both online sending and offline signing?

For example, can I safely:
1. Have both a watching-only and standard wallet in persistent encrypted storage.
2. Start tails with persistent storage and internet connection active.
3. Open watching-only wallet and create unsigned transaction (save to storage).
4. Reboot tails with persistent storage active and internet connection inactive.
5. Open standard wallet, enter passphrase and sign transaction (save to storage).
6. Reboot tails with persistent storage and internet connection active.
7. Open watching-only wallet and send signed transaction.

In this scenario, the password is never entered into the computer while it is online.  Is that good enough, since Tails wipes the computer's memory between boots?

Another scenario:
1. Have standard wallet in persistent encrypted storage, watching-only wallet on 2nd unencrypted thumbdrive.
2. Start tails with persistent storage inactive and internet connection active.
3. Open watching-only wallet and create unsigned transaction (save to 2nd thumbdrive).
4. Reboot tails with persistent storage active and internet connection inactive.
5. Open standard wallet, enter passphrase and sign transaction (save to 2nd thumbdrive).
6. Reboot tails with persistent storage inactive and internet connection active.
7. Open watching-only wallet and send signed transaction.

In this scenario, the persistent storage is never enabled while the computer is online so the computer can't even "see" the electrum wallet while it is online.  Is that good enough?