You can get a light diffuser, which most people use, at the hardware store and cut them to the dimensions of the tank and build all kinds of shelving if you want it. Zip ties work well for holding them together. You can use PVC pipes for legs, drill holes and use zip ties to hold the diffuser on. Both lights would work, but I would go with 250s. The 400s would be a lot of light for zoanthids, maybe too much. Plus you can always get the zoanthids closer to the lights with the way you set up your shelving.