There's technically no problem in reusing it.

Each wallet address contained inside your signal signature wallet is unique and thus the public key, that may have been exposed, has no bearing on your multi-signature setup. Especially since the derivation path is completely different and it is part of a multi-key setup. Obviously it's important to keep your multisig xpub private.

Even if that single signature seed phrase had been compromised, without your knowledge, making it part of a multi-sig protects your wallet, albeit not a perfect setup.

You can also get a little advanced and make your original single signature seed phrase have a passphrase as part of the multi-sig setup.

Yes, avoid reusing a single-sig key you've used for years in a new multisig setup.

Your public key has been exposed on-chain every time you spent from it, giving attackers a head start if they compromise another signer or break quantum resistance later.

It also links the multisig back to your old addresses and activity, killing privacy.

Mixing it in messes with clean backups, separate seeds, and proper multisig derivation paths.

Best move: create fresh seeds on new hardware, sweep your funds over, and retire the old key.

also descriptor/derivation mismatch. Single-sig typically uses BIP84 (m/84'/0'/0') paths; multisig uses BIP48
(m/48'/0'/0'/2').

This is a good question.

There might be technical stuff that I don't know about, but I think the main concern is that you might be linking the years' worth of transactions you have already done to your new multisig.

Since you are creating a new wallet anyway, why not start fresh and clean and try not make the link between the new wallet and your old wallet too obvious?

The best advice I've read today. @theonceler, thanks for asking. The questions raised here help all of us who are still learning.

Use the same seed but the standard multisig derivation.