I've never been a fan of storing seeds on digital devices, even if they're encrypted, and never touched the internet. There's just too much risk of that device failing, but also potentially being compromised prior to you receiving it. Each to their own, however USB's are much more fragile, and don't tend to live as long as pieces of paper stored correctly.

Yeah, LUKS can be used. Although, you still have to trust the hardware that you're setting LUKS up on. I personally wouldn't recommend untrusted one's. However, these days it's hard to even trust well known brands.