@Reynard, one of the fun things IMHO about Fabula Ultima is that joy of building your character. It's a bit like 3e/PF2 mulitclassing, though I would say that it's multiclassing done well. Characters have "classes," but these classes are more like thematic packages of abilities. You grab these abilities as you level, and not necessarily in a particular order. You master your class after 10 levels, and gain a heroic skill, but you can't progress any further in those classes after that point. You can have a max of three non-mastered classes.
So let's create a party of starting characters. Starting characters start at 5th level and must take 2-3 classes.
Markus, the Generic Game Hero
Guardian (2 levels): Defensive Mastery 1, Protect
Spiritist (1 level): Spiritual Magic (Spell: Soul Weapon)
Weaponmaster (2 levels): Breach, Counterattack
Ophelia, the Priestess of Light
Orator (2 levels): Encourage, My Trust in You
Spiritist (3 levels): Spiritual Magic (Spells: Cleanse, Heal, Lux)
Vera, the Gambling Gunslinger
Entropist (2 levels): Entropic Magic (Spell: Gamble), Lucky Seven
Rogue (1 level): High Speed
Sharpshooter (2 levels): Barrage, Ranged Weapon Mastery 1
Garik, the Leaping Lancer
Elementalist (2 levels): Elemental Magic (Spells: Soaring Strike, Elemental Weapon)
Guardian (1 level): Fortress
Weapon Master (2 levels): Bladestorm, Melee Weapon Mastery 1
Aldarus, the Black Mage
Elementalist (3 levels): Elemental Magic (Spells: Fulgur, Glacies, Ignis)
Entropist (1 level): Entropic Magic (Spell: Drain Spirit)
Loremaster (1 level): Insight
Notice that we definitely have overlap between characters. Several characters have levels in Spiritist, Elementalist, Guardian, Weaponmaster, and Entropist but with basically no overlap of abilities. But we have also created fairly different characters in terms of the sorts of things that they do.
Classes in Fabula Ultima
Core Rulebook (15): Arcanist (Summoner), Chimerist, Darkblade, Elementalist, Fury, Guardian, Loremaster, Orator, Rogue, Sharpshooter, Spiritist, Tinkerer, Wayfarer, Weaponmaster
High Fantasy Atlas (4): Chanter, Commander, Dancer, Symbolist
Techno Fantasy Atlas (3): Esper, Mutant, Pilot
Natural Fantasy Atlas (4): Floralist, Gourmet, Invoker, Merchant
Bonus Content (2): Ace of Cards, Necromancer
You do have to be careful about mixing content, especially across the Atlas materials, because they represent different genres and/or sub-genres.