Help refine the magic items for an upcoming campaign

[Meepwizard]

In a soon to be starting campaign I've created these rings in the campaign world and in real life(not actually metal as you can guess). The idea was that after talking to each player separately nobody discussed becoming a full castor. To allow this because I don't want to punish them for being the character they want to be in the world there were rings forged, each ring was made with a specific thing in mind(the red one gets fire spells, and so on...) each player will get one, and important npc's/bosses will get one as well. Each ring gives the wearer access to spells as the player levels up(say they leveled up and got to the level that a wizard would get fireball, the player with the fire ring gets fireball once a day, and so on with other fire spells). The idea was that the players could choose their classes without worrying about having a healer, a wizard, etc... do these seem too much? I understand that they'd be powerful against by the book creatures, but i have several counters to that:
1. If everyone has one in the party nobody will be overpowered compared to other party members
2. This explains why nobody else goes out to stop the world ending thing. These rings have plot powers that allow the players to save the world
3. As they become more known eventually everyone will know about "the great hero joe and his ring of fire", and would plan accordingly(having a bucket of water nearby just in case, etc...)

Finally, I'd like your help to come up with unique power for whatever ring pops into your head of anytype, or maybe some curse. Anything you can think of. Although to alleviate worries some of the rings will happen to be phylacteries to the group of liches(litchi?) that seek to destroy the party.
This is my first campaign and I want the players to have fun

[Vaz]

What level are you starting? What are the player's tendencies and builds?

The simplest thing to me would be to have each Ring inhabited by the weakened soul of the Lich, who knows that they are lost (The one ring style) and desire to be found by their master. As such, they grant immense power to their bearers. Each ring acting as a phylactery boosts the capabilities of the party. As sentient weapons, they can choose which benefits they provide - as in it's yours, as the DM's. This might say allow an evoker to cast their spells dealing fire damage as if it was 1 level higher than the slot they chose, or casts Magic Weapon on the wielder.

As it's a sentient item, it could have its own actions which makes it more useful, you can update on the fly and gradually improve, as well as provide some later discussions as you force players to make a choice between the item, and having deadly fights which could cost members of the party their lives.

[Kane0]

Soudns easy enough. Most parties will be fine regardless of class composition so worry more about flavor than rounding out the capabilities of the party. Shortcomings make it more fun anyways!

Each ring possesses one charge per two levels of the wearer (minimum 1) and requires attunement. You can spend one charge to gain advantage on a [skill] check which differs for each ring. During a long rest the ring regains all expended charges.
At first level the ring grants access to one cantrip.
At level 3 it grants [one first level spell] (one charge to cast, one extra to upcast)
At level 5 it grants [one second level spell] (two charges to cast, one extra to upcast)
At level 7 it grants [one third level spell] (three charges to cast, one extra to upcast)
And so on. The skill and spells differ for each ring to match whatever theme you want.