1. Lets say I start by purchasing 1 BTC on Coinbase, which I pay for with my VISA. As this is such a well known exchange which requires KYC and probably has established ties to various authorities, I'm guessing it would be fairly simple for them to trace this initial purchase back to me.
Correct. Coinbase knows your identity because you underwent KYC with them. They will also know from where you deposited your fiat, the address your BTC was sent to on Coinbase, and the withdrawal address you withdrew your coins to.
2. But then I transfer this 1 BTC onto my personal Ledger wallet, where I already have 2 BTC. On my end, I can easily see that I have 3 BTC. But as Ledger will usually change the receiving address so as to spread the deposited funds across several addresses, will anyone else be able to see that I have 3 BTC, or will they just see that single 1 BTC?
If you send the coins from Coinbase to the same address where you already have 2 BTC, you will be connecting those two UTXOs. Anyone can see that an address that previously held 2 BTC has now received another deposit of 1 BTC. If you send the 1 BTC to a new address generated on Ledger, Coinbase won't know that you have 2 BTC on a different one.
3. Now I take 1.5 BTC on my Ledger and swap them over to ETH, which will give me approximately 21 ETH at the current rates. Will outsiders still be able to track and make heads or tail of this transaction, as it will draw funds from both of my BTC addresses and end up on a different blockchain?
Since you sent coins from different UTXOs and you were able to sign that transaction, that's proof that the coins in both those addresses belong to you. Coinbase and the public can check that the 1 BTC that was initially withdrawn from Coinbase was combined with another UTXO. Therefore, both belong to you. Additionally, if the transaction was sent to another centralized exchange, blockchain analysis could potentially discover which exchange that is, based on consolidated transactions to one or more of their wallets. Since most CEXs require KYC, government agencies could request the name of the account holder.
4. And then I further go on to transfer my 21 ETH on to Metamask, where I will use a DEX to swap it over to approximately 183 wBNB. It will still be on the ETH blockchain of course, and the same Metamask address too. But it will now be a different token, so can outsiders still be sure that it belongs to me?
The trail can still be followed to your MetaMask address, but unless that address has been connected to a service that required KYC, it's impossible to tell if it belongs to you. You could have used those coins to purchase some goods or services and it belongs to the merchant. I am not sure how the MetaMask DEXs work, so I can't comment on what happens next. I would assume that it's still public information and that you check the blockchain that someone exchanged 21 ETH for wBNB and those wBNB tokens were sent back to the same address from where the ETH originated from.
5. Then I use a blockchain bridge, to migrate my wBNB over to the BSC. This means the tokens will be swapped over to BNB and also on a different blockchain. Could prying eyes still keep track of this?
I don't know, but I don't think so.
6. I then take half the BNB and swap it over to USDT, before I enter them into a liquidity pool. Now I will have a bunch of liquidity pool tokens consisting 50/50 of BNB and USDT. Is it still possible to trace?
Same as above. Unlikely.
7. I stake these LP tokens in a yield aggregator, where they will be added to a much larger pool of locked funds, and automatically reinvested 3x times to earn compounded interest, which I will then harvest in the form of CAKE tokens. But these CAKE tokens will be deposited to the same BSC address I used earlier, so does that mean it would be easy to understand for anyone else just what has transpired?
I don't know how those liquidity providers function but they are all part of decentralized finance. You won't be asked for identifiable information according to what I have read and heard.
I then swap the earned CAKE tokens back to BNB, and transfer them on Binance, which is of course again a well known exchange with KYC and probably established ties to authorities. But would these authorities be able to know that the receiving address belonged to Binance just from looking at the blockchain? And if they did, could they tell who owned the specific account?
When it comes to Bitcoin, Binance consolidates their funds in various hot and cold wallets. That's how blockchain analysis can determine that an address belongs to Binance. I would assume that the same thing happens with BNB.
9. I sell these BNB to USD, and transfer them to my old school bank account via SEPA, which should be a dead giveaway I suppose. But would anyone be able to see that the USD I receive stems from my initial 1 BTC purchase over at Coinbase?
Too many things have happened in between for anyone to make that connection. I am not an expert in these matters, but I don't think such a connection could be made.