1) Usb keys are known to be capable of having viruses on them even if they are not connected to the internet.
As far as I understand the infamous Stuxnet virus operated like that.
2) seems like a massive hassle to type things manually from an air-gapped machine.
3) In my opinion having such concerns kind of ruins the point of purchasing a special BTC hardware wallet. If you need the wallet and additionally need an air gapped machine you may as well just purchase a different hardware wallet that is less of a hassle eg. a trezor or a Case hardware wallet etc
I guess it may have the same result but I would pay more to have less steps to perform. a simple solution but a lighter wallet XD
1) if you need to be that sure, then don't use USB
2) you can't be bothered to type 58 characters manually once for a longterm cold storage solution with (almost) 100% security?
3) trezor or case are something completely different and have other attack vectors