You should look into a manufactured wet/dry filter for your tank rated for the capacity of your tank or larger. It is liable to hold more water than your proposed sump and will be set up for efficient nitrification. If you wanted you could add bioballs to your overflows, it won't be the most efficient for nitrification....but it will keep them quiet. I, as a preferance, find it unsightly and difficult to service. Eventually the bioballs will be coated with brown bacterial slime that may clog the overflows.