I would use bio balls in the first but not plants, the flow rate through would probably not be conducive to keeping them. A sump is a great place for a heater to get it out of sight, could also use the second compartment for any reactors, skimmers or other equipment.
Looks to me like the middle divider is going to restrict the water flow through water ever media you choose. Most the water will just travel over the top of the media and over the middle divider. Unless i'm not seeing it right in the two shots.
Looks to me like the middle divider is going to restrict the water flow through water ever media you choose. Most the water will just travel over the top of the media and over the middle divider. Unless i'm not seeing it right in the two shots.
Also without a drip tray the bioballs won't do much good. You need to be able to drip water across the top of all the bio balls. The way you are set up you'l have submerged media, so ceramic rings or pond matrix would be a better choice.