I like the 2nd crypto idea. if I understand it correctly to:
1. do the slow USD bank transfers to an exchange
2. buy a stable crypto of some sort
3. download it to hardware wallet
(possibly repeat steps 1-3 a number of times to avoid a large single transaction)
4. When ready to buy BTC, upload stable crypto (I assume this is fast?)
5. buy BTC and download to hardware wallet.
would Coinbase be good for this?
Seems like you are going with my idea. I want to ask you a question, have you ever purchased bitcoin in past using bank transfer? How do you know it will be slow? In India, I can send funds from my bank account to the exchange's bank account using 'mobile banking application' and Indian Rupees balance reflects instantaneously on my exchange' account. I can then use that balance to buy bitcoin and the whole process hardly takes 2-3 minutes.
Coinbase doesn't allow buying facility in India so I have no idea about it. But I guess US exchanges like Coinbase, Kraken, Gemini, etc. also provide same facility and you can buy bitcoin using bank transfer instantaneously as well. However, I am not sure about that.
But in any case, if bank transfer is slow for you, you can surely follow the idea of stablecoin like I advised earlier. You can buy Tether or any other stablecoin on the exchange (I have no idea if Coinbase allows purchase of stablecoin with bank transfer or not) then transfer that to a hardware wallet (you will need either Trezor or Ledger hardware wallet for that).
Yes, sending stablecoin back to exchange is usually fast. For example, currently sending USDT on ethereum blockchain will take 3-4 minutes using $0.36-0.40 fees. You can buy bitcoin with that and send bitcoin back to the hardware wallet.
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I will go with your advice, but one more comment to make. It will be good for the OP to just make use of Dex that can be found on the noncustodial wallets directly that support no kyc or any other verification. Like, if he is using Trezor, he can make use of binance Dex for the exchange ont the trezor wallet, and on many other noncustodial wallets that support many cryptocurrencies, that support bitcoin and tether, the exchange can be done easily if it support Dex. And, in the process, only mining fee will be charged during the process, and it will not take more than 10 minutes to 20 minutes. Although, this is not good for flexible trading, which he can then follow using no kyc exchange.
Are you sure you can purchase Bitcoin on DEX? I don't see any possible mechanism for that. The maximum you can do is purchase bitcoin-equivalent on other blockchains using DEX. For example, you can buy bitcoin BEP2 on Binance DEX. However, that is not real bitcoin. It will only be available on Binance blockchain and not possible to transfer to other bitcoin address. It is more of a synthetic bitcoin.