Speaking from personal experience, I would not set up a tank with Eco-Complete. I have Flourite in my 70g, for two years now; these two products are basically the same, and I have been extremely disappointed. The same plant species in this tank are no better than those in my sand substrate tanks. Liquid fertilization is still mandatory. Some even suggest using substrate fertilizer tabs, which I do in my sand tanks for the larger swords; this should not be necessary with enriched substrates, but the point only goes to show how ineffective they are for the incredible cost. Then there is the problem with substrate fish. I chose Flourite over EC solely because of the roughness; in my hand the F felt less rough than EC. But I had to remove the corys after they developed mouth and barbel issues, and after a few weeks in the sand substrate tank they recovered fortunately and are now doing well. Even after almost 2 years, when I am working in the substrate, the Flourite is still sharp enough to scratch my hands. If you don't open the bags, you can probably find someone to buy them perhaps at a slight discount.
Moving on to light, unless you intend diffused CO2, you will not want more than two T8 full length tubes. I have this over my 4-foot 70g and 90g tanks and my 5-foot 115g, and it is sufficient for most plants. I have to control the duration or algae increases, which is always due to light beyond what the plants can use. You can see the state of my tanks in the photos, click "Aquariums" tab below my name on the left. I follow the method in the series stickied at the head of this section that you earlier mentioned, so that is the result.
I agree on the carbon (don't use it). As for pH, don't fiddle with that, let it lower naturally which is likely will. Tied to this though, what is the GH and KH of your tap water?