The cocofiber will absorb a lot of water but it does not supply nutrients as the fibers are very long lasting. I use cocofiber in my mix at 25% of the total. I do like the way it performs, especially the lifespan.
I have no experience with worm castings but they should be helpful. Some people like to put slow release fertilizer granules in the soil. These ways of supplying nutrients are not going to last forever. If you're dead set against watering with nutrients, and still want to go soilless, then you might have to repot periodically to refresh the nutrient component of the soil.
