Best Practices: After mixing, how to send coins to a watch-only wallet?

[ghscuuo]

First, thanks for making mixing so convenient. I really appreciate it.

Now that my Wasabi wallet Privacy Progress is 100%, I want to get my coins out of my hot wasabi online wallet as securely and anonymously and quickly (in that order) as possible, into the xpub of an offline wallet that has never had its keys online.

1. I don't intend to ever spend these coins.
2. I'd like the offline watch-only wallet to be taproot.
3. I'd like the coins to be consolidated into a "pyramid" of utxo sizes, with many 1M-sat utxos at the base, with some 3M-, 10M-, and 30M-sat utxos in the middle, and a very small number of 100M-sat utxos at the top (distributed like one might have with denominations of paper fiat in a leather wallet).
4. I'm scared as heck that I'm going to break my anonymity if I don't do this correctly.
5. I'm familiar and very happy with Sparrow wallet if that helps.

How best to accomplish something like that? Suggestions welcome. Thanks again.

[Kruwed]

Thanks for your interest in Bitcoin privacy and insightful questions!

I don't intend to ever spend these coins.

If you do ever need to spend those coins for some reason, try to send the entire UTXO out of cold storage without creating a change output. Otherwise, you would have to send that change output back to Wasabi to coinjoin again and it would be tedious/expensive.

I'd like the offline watch-only wallet to be taproot.

No problem, there shouldn't be any privacy issues with that.

I'd like the coins to be consolidated into a "pyramid" of utxo sizes, with many 1M-sat utxos at the base, with some 3M-, 10M-, and 30M-sat utxos in the middle, and a very small number of 100M-sat utxos at the top (distributed like one might have with denominations of paper fiat in a leather wallet).

You can choose your own UTXO size and destination address with the PayInCoinjoin feature available in Wasabi's RPC. It's possible to send small or medium sized amounts this way, UX improvements and the GUI part are still being built.

I'm scared as heck that I'm going to break my anonymity if I don't do this correctly.

Put yourself in the perspective of an attacker/spy: Are they considering the proximity of your UTXOs within rounds, or the timing/volume of coin movements?

There's 3 aspects of UTXO proximity to consider:

A: Preventing input to input links
B: Preventing input to output links
C: Preventing output to output links

A is handled by the "Red coin isolation" feature. If you have an extremely large amount of BTC compared to the rest of the coinjoin participants, then the "exclude coins" feature can be used to further limit the amount of liquidity you send into a single round.
B is handled by remixing. Increasing your anonymity score target will add more distance between the coins you receive and the coins you spend.
C is probably the trickiest for users to handle. Consolidating coinjoin outputs in payments obviously reveals the same user owns them, but this action is only a marginal privacy loss, not a deterministic link. PayInCoinjoin is the best solution for this.

Timing and volume analysis of coin movements is mitigated with extra randomness provided by the client, Whenever you transact and create nonprivate (anon score 1) coins, Wasabi will automatically remix some of your coins that have already reached their anonymity score target. This resets the age of those coins and morphs the total amount you receive from the coinjoin so it doesn't match the value of the nonprivate coin you intend to anonymize.

One thing to consider is that ~98% of coinjoined UTXOs are spent or remixed within the first month they are created, so you want your behavior to blend in with the rest of the crowd. You can increase your privacy by waiting ~1-7 days in between coinjoin rounds, but if you waited several months between your coinjoin rounds, you would probably decrease your privacy.

You didn't mention it, but another pro tip is to avoid starting the coinjoin input registration if you know you will have to pause it later. Abandoning or disconnecting a coinjoin round leaks a small amount of metadata to the coordinator and/or other coinjoin participants (depending on the phase), so try to complete rounds if you've already registered more than 1 input to it.