I like the idea of candle, it could be a new craft for the advanced agriculture skill with beehive, like crafting recipe to melt honeycomb into pure wax with a pot and a fireplace, wax can be used by material prep or forging skill to craft candle recipe with wax, grasscords and copper lumps.
In my opinion copper need more common use in the game and candle can be a new way to use it, like copper decorations outfit (copper crown, copper jewels).
But candle mean more player's objects in the world, mean more in-engine light sources, more data and maybe more lags.