[OJFord]

Well, you need more than one.

And I locked myself out of the first one while (before finishing!) setting up my second, so IMO you need more than two.

(It's not a great story, the tl;dr is I used a different passphrase for the second one, mixed them up, and ploughed through my 3 tries at the passphrase on my first one confident I was getting it right.

I also think that default (Yubikey's) of 3-tries is insanely low, getting it wrong just once is nerve-wracking; how much easier is it to brute-force in 30? That's more guesses of pet names et al. sure but you're not brute forcing it in that. Just don't use a pet name.)