Hi and welcome to TRT! Since this is going to be a reef I would second the suggestion to get rid of the bio-balls. They
trap detritus which continues to rot in the water column releasing all the nasties that cause problems. All you need for filtration is Live Rock (LR) and a strong skimmer.
The baffles in the sump serve a feww purposes, the main purpose being to discipate bubbles before the return pump can shoot them to the main tank. A series of over and under baffles will help do this. Its important to keep the baffles far enough apart so the water doesnt have a high velocity as it passes. This will prevent the bubbles from being taken along for the roller coaster ride and getting returned to the tank. Keeping the design simple is the best thing to do also. Here is a pic of a 20Long I used as a sump on a 55 and an
acrylic sump I made for my 150. Do a search here for "sumps" and you will find enough reading material and pictures to keep you busy all day! Welcome to TRT!
Robert