How many character classes should be available in a pen and paper JRPG game?

Right now, I assume I'll be designing missions to engage up to 4 Adventurers and 1 Dungeon Master, so up to five total players. I have six total player classes to choose from for the (up to) 4 adventurers so far:

Barbarian

Paladin

Thief

Mage

Cleric

Summoner

Additional Classes I might consider adding:

Ranger

Monk

Illusionist

Enemy monsters include some typical fantastic creatures and a few inventions of my own:

Goblins

Orcs

Trolls

Chaos Knights

Demons

Skeletons

Lich

Demi-Lich

Vampire

Brain Eater (steals your spells every time it hits you.)

Dream Devourer- A more powerful type of Brain Eater

Harlock, the Warlock - Primary Antagonist

Red Dragon

Black Dragon

How many character classes should be available in a pen and paper JRPG game?
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