Yeah, I would merge some of those into one category as well.
Detection - spells/powers that detect things
Divination - spells/powers that allow viewing of the future utilizing at least one sense (vision), but may include others
Informational - spells/powers that divine information about items, persons, etc
Scrying - spells/powers that allow viewing of the present utilizing at least one sense (vision), but may include others
Alchemical - spells/powers that deal with the creation of magical potions, gases, chews
Enchantment - spells/powers that deal with the creation of magical items such as rings, weapons, staffs, wands, etc
Enhancement - spells/power that improve or increase what already exists (In items I presume.)
Transmutation - spells/powers that change the fundamental structures of substances
The reason I said it sounded familiar..
In 1st ed, Mages could cast whatever spells they had and schools of magic were just descriptions in the spells. They didn't have a lot to do with the game. The Illusionist was the only fully formed "Specialist". They could only cast their own specific spells and a few Magic User spells at later levels.
In 2nd ed, Mages
could specialize in a specific school of magic. This choice was made in chargen. Some schools were related and others opposed. Related might translate as Open in RM and Opposed are Restricted; maybe Own Realm Other Base and Restricted.
Illusion\Phantasm
Alteration\Transformation Enchantment\Charm
Divination (Lesser\Greater) ✵ Conjuration\Summoning
Invocation\Evocation Abjuration
Necromancy
The above chart is supposed to be circular. If you specialized in Illusion, then you could also learn Alteration and Enchantment\Charm, but never Necromancy.
If you were a Conjurer\Summoner, then you could cast Enchantment\Charm and Abjuration but never Divination.
The benefits of this were a bonus to spells\saving throws (RR) plus an extra spell for each level of spell you could cast. In RM, this would be extra PP, I guess.
The real reason I bring this up is RR and game mechanics.
Will each of your 27 types have different RM game mechanics or follow the standard E, BE, DE, F, P, U, I and s, m?
I'm not being snarky, it just sounds like a daunting task.