Substrate is whatever ends up on the bottom of your tank, the category includes gravel, soil, clay, sand, etc. It doesn't necessarily refer to capping off soil or enriched substrate with yet more substrate. That gravel should work well, but keep in mind that if you get rooting plants like crypts or swords, you'll probably want to put root tabs under the plants so that they can absorb nutrients that way. Plants like anubias, java moss, java fern, hornwort, etc, feed from the water column, so root tabs aren't necessary.
The reason why I dose Excel every day is because it's not the same as the micronutrients you're dosing--those only really need to be added once a week. Excel provides the plants with carbonates in liquid form, and these are consumed much more quickly, especially under moderate-high light. In this way I use Excel in lieu of CO2.