Hey Derek....welcome to plants and plantedtank.net!
It seems like the more you learn the more there is to learn in this hobby. That said, substrates can be tackled from so many points of view, in so many ways. Any opinion you get on this one is merely that: opinion.
I would say the following: don't put anything ON TOP of hte eco-complete, unless you don't like the color. I personally love the black look, and I would leave it there for asthetics.
As for layers under the eco-complete...several options come to mind. I've heard of Laterite, peat, kitty litter, soil, mulm, etc. I think it's really, really helpful to use old mulm/detritus from an established tank here. It helps the substrate age faster, which will lead to a more stable tank faster. Peat....I'm really not sold on that, not sure exactly what benefits there are in that. Laterite, provides and excellent source of nutrients to the roots over time, mostly Iron I think.
But the short answer: eco-complete is just that "complete". You don't NEED to add anything!