Adding things like clay or clay based products (kitty litter springs to mind) can add cec but its not needed to grow lush healthy plants. Balancing nutrients, plants, and light is everything. The nutrients will come from your fish (if you have fish) and fertilizers. You don't need clay for this.
I am not familiar with your light or lights in general to comment on it. If you have seen people growing similar plants with this light in similar sized tanks than its probably fine. I didn't notice on that website any mention of par values or cri which would be a nonstarter if it was my tank. But it is significantly cheaper than a fluval 3.0 which seems like the popular off the shelf choice these days so /shrug.