But, like, even considering the extortion, wouldn't it be better to only sell when you really need it, instead of keeping fiat money idling in the bank where it will lose way more than 15% of its purchasing power in three years? Bitcoin on the other hand will appreciate way more than 15% in three years. 

 You are right then, I did not understand, nor I am sure I do now though.
Do you mean that by selling and immediately buying again, you reset the capital gain so that, when you sell it again in the future, it will be calculated on the second purchase price, hence taxation will be on a lower amount?
 

 that is smart alright, and there is no custodial business involved either, except the minimum required time the coins are on an exchange, so win-win. 

 If you can pay off the mortgage with cash, selling F2F will pose some risk for new contacts, but will let you stack some paper useful to that purpose after you put in place a vetting procedure for prospective buyers.
For example, you could require the buyer to have a video chat with you on jitsi, so you can check him out before actually meeting in person. 

 Bisq2 and Bisq1 are different applications, the latter is only using the new Bisq Easy trading protocol for now, and is aimed at nocoiners.
If you like the multisig protocol, as everyone does, you can keep using Bisq1, and wait until that will be ported to Bisq2 in its musig taproot version with less onchain costs and improved privacy. 

 Bisq is the most decentralized on-ramp and off-ramp exchange there is. 

 Make sure to read bisq.wiki and learn the ropes plus memorize the trading rules, the experience should be downhill from there. 

 It also depends on the market liquidity for stablecoins trades on Bisq. Fiat market is much more active. 

 It is true that Bisq trades can be identified on the blockchain because of the characteristic inputs-outputs distribution, but from this to calling it a privacy nightmare there's a lot of space.
As usual all depends on your threat model, yet you can obtain a very reasonable privacy by either using unlinked btc utxos to pay for fees, or not linking trades with too many bsq peeling transactions.
Coinjoin is also a very good option, and I am talking about Joinmarket here, which is the only properly decentralized coinjoin implementation in existence (dont' be fooled by search engine hits, it's only on github). Joininbox runs a contained JoinMarket instance from a SD card on a raspberry pi3, with a pruned btc node.