There is a space in folklore for a wise man or woman who knows something of potions and lotions, first aid and surgery, herbs and metals, religion and curses, languages and relics, and what to do about the "simple" supernatural problems faced by regular people.
This person has some spell-like powers but no spells. Everything is subtle.
I think the way to handle this is to have two sets of abilities.
One system is granted powers, like the ability to find missing objects, to read spell scrolls, or to turn undead.
One would pick some set of abilities and then assign each one a level at which the character could perform the thing.
The other one is to be able to prepare spell-like powers in the form of apothecary concoctions. These would be perishable so they would need to be replenished every so often even if they were not expended - some per diem and some weekly, etc., depending on the kind.
In this case, each kind could be assigned a "spell level" before which the person could not learn it. But I don't think that the preparation should be Vancian in nature, but rather something akin to spell points. Call it Rx Points maybe?
There could be several disciplines and each one could have access to a few unique concoctions, to emulate specialist wizards and clerics.
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This all seems more complicated than OD&D but not as complicated as 3 or 4e. It's in line with 5e complexity I think. Not outside the limits of OD&D.
Has anyone got any criticisms or suggestions?