Looks ok. Bio-balls aren't really needed in a medium to heavily planted tank, but shouldn't hurt anything. I only have mechanical filtration in my sump. I'll add in chemical after I dose meds, but I don't leave it in all the time.
Laying the heater flat is a good idea to keep it fully submersed all the time. Most people put their CO2 reactor in the return line after the pump. Having a submerged pump in the sump is the easy way to go, but you can go external as well.