A pc that you basically don't connect anywhere and not use for anything other than for storing coins seems like the best bet in buying Bitcoin anonymously. It's much more privacy based compared to buying HW wallets, since as you say, they can trace you if you ever bought one. As for emails, dude you can create a ton of emails, not really something they can trace to you if you actually tried to.
The final answer to this whole question of anonymity, especially as it concerns privacy concerns seems, that no matter what they will know or guess that you bought some of this privacy coin, but as a last resort if they came after you, you could say, oh sorry, I lost my private keys and lost the coins. What are your opinions on this?
Yea I think that works. As long as you don't give them the device that holds your coins, they can't really find out and afaik if they don't have a warrant, they can't ask to even inspect your stuff. Hardly doubt they'd actually give a warrant for only a "guess" so the only time you'd get a warrant is that you effed up on something and they have hard proof that you bought Bitcoin.