Noisy Kricket, welcome to Tropical Fish Keeping forum.
As a general guide to a natural or low-tech planted tank, have a read of the 4-part series "A Basic Approach to the Natural Planted Aquarium" stickied at the head of the Aquarium Plants section.
Now to some issues you mention specifically, beginning with the substrate. I gather you already have the Eco-Complete. Corys do not do that well over this, it may be the sharpness or it may be other things as well. Flourite is similar, I had to remove the corys from my tank with Flourite. I am also very disappointed with the lack of any perceivable benefit of these over plain sand or fine gravel.
Second thing is Excel. I do not recommend this or similar products. API CO2 Booster is 1.6% glutaraldehyde (rest is water). Seachem's Excel is the same but a slightly higher percentage. This chemical is toxic. It is used to disinfect medical and dental instruments and as a chemical preservative. Considered a hazardous substance, skin irritant, toxic if inhaled, etc. You can read more here (which comes from a link on the API website): http://cms.marsfishcare.com/files/ms...ter_081810.pdf
It kills cells, and is used in products that attack viruses and bacteria. So, it may well affect bacteria in an aquarium. It will kill some aquarium plants outright at normal dosages, Vallisneria is one. If dosed at high levels, it will kill fish.
I've no experience using LED systems so can't offer anything on that. The mentioned plants are all low-light. If you have the plants in from the start, it will help with the "cycling," but i would recommend adding some floating plants which are especially good with this. Not to mention that all forest fish prefer a "roof" over them anyway.