I find that sand substrates are good for stem plants that have thinner roots. Using large gravel doesn't make the best substrate for plants, there isn't much for the roots to hand onto and it seems to take longer for them to get established IMO.
I'd personally use a sand substrate with flourite black sand underneath. The flourite hold many nutrients as it is like river silt and the sand on top will keep the dusty flourite from getting in the water column and making a mess. Wouldn't be a bad idea to watch some youtube videos on how to set up nano planted tanks. You'll get more ideas that way.