RE: What's The Best Way To Manage Rentals?

You don't need a spellbook unless you want to play with the account and earn rewards. But you should log into that account with Splinterlands to be 'marked' as a Splinterlands account. Otherwise, if you want to transfer cards to that account from PeakMonsters, it will tell you the account exists, but it's not a Splinterlands account.

A few intermediary steps.

1.a. Ask GenepoolChlrn8r in their discord to add your account as a management account. He is usually quite responsive. It's the only time you actually need to interact with them unless you want to.
2.a. Delegate HP to the new account. They say 100 HP per 100 cards. Lower if the number of cards is higher (meaning less than 100 HP per 100 cards). The interface will tell you exactly how much it needs, once you add the cards.