I've just taken over a hotel and want to clear out the previous operator's archive. I now log reservations electronically — can I throw away the old reservation registers, or store them in a warehouse off-site?

No — don't. Under the Identity Notification Law and its regulation, having taken over the business, you are now responsible for the previous operator's registers too, and the same regulation requires reservation registers to be kept for 5 years starting from the year after the year they relate to.