to start using a new hardware wallet, can I transfer hex + stakes to a new address (protected by hardware wallet), or can I only migrate my existing keys into HW wallet (but I'll be less sure about their security because they were originally generated in metamask)?
Stakes you created with the initial metamask SEED are really something to worry about. You never know when someone might get ahold of your keys. Always install MM and keep a record of the initial SEED, just in case you used this wallet accidentally. BUT connect a hardware wallet and only use its address(es) for stakes, not the initial MM SEED.
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