I’m not sure how multiclassing and spells is working in this game, there seems to be some contention and uncertainty in that regard.
But it will not work how you are envisioning it.
In 5th Ed your spell slots are shared amongst all your classes. No matter how many caster classes you have, you can never have more than 4 slots per level. Spells you know can be cast with any slots.
The only difference here is warlock I believe. I think their slots are different, but they can still cast any sort of spell with any sort of spell slot. I need to refresh myself on those rules.
