I'm not sure of any hardware wallets that you can import a priv key, and you dont trust hardware wallets maybe.
Even if you could, you would be slightly reducing your security by importing a key from a properly airgapped system into a hardware wallet that is connected via USB to a desktop machine that is online. But forget about private keys, that's in the past. Use seed phrases.
1.import private key to electrum airgapped
2. Look what address appears.
Import the key from where? You are going to create a new wallet on your airgapped system. That's where you generate your seed and the private keys. Don't import a private key from somewhere else. It's not going to be a key you created in an airgapped environment, unless it came from another cold wallet.
3. Set up electrum watching wallet for that address only on other internet live machine see balance.
It's bad for your privacy to use only one address to receive all your bitcoin transactions. Everyone who knows that address belongs to you, can keep track of how much bitcoin is on it.
4. On airgapped wallet select spend but untick use new change address ( this is because if I'm not wrong the drawback with starting on an airgapped wallet is it doesnt update its memory of prior tx until you submit and it gets confirms which it cant do airgapped.
Right. Your airgapped wallet won't display your UTXOs because it's not connected to the internet or Electrum servers. It can't retrieve information about your UTXOs. You'll have to create transactions on the online wallet and use the cold one just for signing purposes.
Are uxto the same as addresses?
No. You can have multiple UTXOs on the same address or spread around on different addresses. When it comes to spending, it makes no difference to the network. Spending from different addresses doesn't cost more than spending UTXOs from the same address.
Maybe even when change is issued to the same spending address.
Like I said earlier, using the same address over and over again is bad for your privacy.
5. Export the signed tx with qr code.
At this point nothing has been put on the cold machine only a qr code taken off from it.
Not exactly. Before you signed the transaction on your airgapped wallet, you must import the transaction you created on your online wallet via QR code, USB or Micro SD card. Only then can you sign it on the cold wallet and export the signed transaction to be broadcasted on the online wallet.
This is the tricky part to understand as to how you start a spend with a cold wallet not start with a psbt from a watch only.
You can't. It has no connection to the internet, so the wallet contains no information about your UTXOs. It only has the signing keys.
The second part is the fees. I guess just look at the network congestion and put a good fee.
It all depends on how fast you need the transaction to confirm. I use
https://mempool.space/ and
https://jochen-hoenicke.de/queue/#BTC%20(default%20mempool),2h,weight to check how everything looks at the moment I send transactions. If you are in a hurry, you need to set a high enough fee for your transaction to be included in one of the upcoming blocks. If not, you can use the no/low priority fees or even below that if you don't mind waiting. But pay attention to the purging rate, and don't set a fee lower than that.