Thank you so much for your feedback!
You spend a spell slot when you draw, so there are no “additional spells*.”
*see below
There’s an absolute intent that you “build” your spell deck by creating a spell book that only has spells you’d cast in a given situation like combat or daily prep. Every spell in the deck is effectively “prepared” but the ones in the deck are only able to be cast at “random.” If there’s a spell you want to insure you can cast on demand you’d have it prepared normally. At low level, when you’re likely to only have 1 spellbook, you can take spells you wouldn’t want to draw out by preparing them.
The advantage of the deck is that you can occasionally cast upper level spells with lower level slots, or cast spells with terrible casting times as an action though they have some diminished effects.
*You’re also refunded slots of the level difference when you use a higher level slot and draw a spell with no upcast option.