I've been using the spell dice house rule that Brian Ashford​ wrote about; each Wise character rolls their level's...

I've been using the spell dice house rule that Brian Ashford​ wrote about; each Wise character rolls their level's HD each day and gets that many spell points, and a spell costs 1 spell point per level to cast. I've also added that when these run out the player can carry on casting spells at 1d6 HP damage to the caster per spell level.

To help stop this from becoming overpowered I've made Wise characters use an affiliation group (which they cannot add next to an ability) to be able to use spells from a certain section of Wonder & Wickedness (Vivimancy, for example). If they want to us Psychomancy spells, they'd have to wait until they level up and get another group. I'd like to write a spellbook similar to W&W with schools of magic more in line with traditional extra classes, so a Druidry list of spells, a Psionics list of spells, a cleric-style list of spells etc. This would allow the Wise a kind of multiclassing without messing with their class table at all.

I'll let you know how this goes when I run my next session. I've run one session of D&D 5e where all 5 players had never played an RPG before, and I'm carrying on the starter set adventure with everything converted to Whitehack. It'll be interesting to see how the players react to going from near-immortal 1st-level 5e characters to puny OSR characters!