Howdy, Cyara, and welcome to the diy forum! I think your sketch up looks good and the idea for the slo drain draining directly into the wicking bed is good. Our worms love to eat the fish solids. Assuming your liftgates are manually operated, you could water from the top so the good stuff is filtered away from the water as it makes its way thru the growmedia. I think this will make it more readily available to the worms. FIY-composting worms have an aquatic gene (some types worse than others) so if not kept separate from the water they can easily drown themselves. It is not easy finding a material that they cannot eat or move through or that will not deteriorate over time, but a separation between the standing water and the soil along with a constant supply of food (solids removed from the fish tank) will help keep them where they need be.