I replied to your other post re: silica sand, but I'll say it here too....
DO NOT use the silica-based sand! DO NOT! Just like Nitrates and Phosphates, Silicates = HUGE ALGAE blooms. I made the mistake of using beach-sand from here in San diego (silica sand!) in my first SW tank... had massive diatom and hair algae blooms for well over a year, I finally learned about silicates and removed all the sand, didn't have that problem again.
Calcium-based sand has natural PH-buffering properties...it reacts with CO2 given off by the fish/other living organsisms and helps to raise and stabilize the PH, and since in saltwater tanks we want a high PH, thats a good thing. Silica-based sands do NOT have this PH-buffering capability. <-- this is what the "vinegar test' tests for...if it fizz's, then it's a calcium-based sand.
Additionally, you will definitely need a much bigger sump. I would reccommend at mimimum something in the 80gallon+ range. For several reasons: adequate room for skimmer, pump, heater, any phosban/carbon/media reactor(s) you decide you want to use, room for evaporation, etc... Since you've got such a huge footprint to work with, go and buy a couple of huge 50+gallon bins from HD or something, and use those as your sump and refugium. A sump doesn't have to be anything sexy and gorgeous, just has to hold water.
Ditch the bioballs. They are nitrate-producers. And, even as little as say, 15-25lbs of LR will have WAY more surface area for bacterial growth than that ammount of Bioballs, so while the thought that it would lessen your need for LR in the display is a good idea in theory, in practice it won't do anything.
Keeping small sharks and stingrays in a reef tank is certainly doable, but will definitely require some serious thought and planning. Sharks and stingrays are EXTREMELY dirty animals....one 6" round stingray will have the same bioload as say, two or three 6" tangs! You will need excellent circulation and filtration to have any hope of keeping the water clean enough to also keep corals alive. And while they will spend 85% of their time happily along the bottom on the sand, they can go crazy and swim wildly around the tank an knock over anything in their path.... doable, but definitely not easy.