It depends on what you want to do. If you want to do a regular Planted tank meaning just plants and some inert substrate such as gravel or sand, then you'll have to do your weekly water changes and all. If you went with Natural Planted Tank (NPT) then at the beginning before everything settles you have to do lots of water changes until your levels of ammonia, nitrite and nitrate balance out and then after that it's like a water change once a month or so. But you have to have the right soil, a cap like gravel or sand and then fast growing plants to help soak up ammonia.
So it depends on what you want to do and what you want to invest in. Either way you'll need some good lighting so throw out the old incandescent that your tank comes with. A good light would be a CFL (compact fluorescent light) which can be purchased at wal-mart/home depot/lowes and find one that has a Kelvin rating for either 5,000 or 6,500K. 6,500K is what the sun is measured at on a nice clear, sunny, mid-afternoon day at it's peak. That's the best time to grow plants and the best bulb for your plants in the aquarium!
Yeah Eco-Complete is great and would technically be considered an NPT since it's not an inert substrate ^_^ When I think of NPT I usually think of soil based with a cap; so the Walstad method but Eco-Complete is great! IMHO it's easier to move things around with Eco-Complete since you don't have to worry about messing up the two layer's and all. So I definitely recommend it as well if you're like me and like to move things a lot. If you like to just set things and let it run wild, then you might want to do the Walstad method then, I think there's more nutrients or something. Not entirely sure about that and I could just be making things up haha.
So with the Eco-Complete, that's all you'd use for the substrate, no caps needed or anything so it's like a gravel that gives your plants nutrients!