Hi there. I have a very heavily planted tank with medium level lighting. The substrate is Eco Complete, black. I use Co2 injection and Excel (Glut) as carbon sources. I use root tabs for the heavy root feeders like swords and crypts and Flourish comprehensive for the water column feeders like Java Moss and Java Fern.
This is the result:
View attachment 273431
I'm not sure about planting into gravel or sand as there are no nutrients initially, when you want the plants to establish. I stayed away from soil because I have Malayan Trumpet Snails and they gently turn over the substrate when they bury themselves during the day, I think they would bring the soil up through any gravel or sand cap.
You said you would have an air stone to keep the O2 moving but I only have mine on at night, during the day the plants take in Co2 and give off O2. This is reversed at night and I use the air stone to drive off some off the Co2 produced by the plants. I have fish and don't want the Co2 level to rise too high at night. Using an air stone during the day is great for fish but drives off the Co2 and therefore not so good for the plants. It's a balancing act, helped by having daytime lighting, evening and early morning lighting (blue lights), Co2 and air stone all on timers (4 in all).
I'm not saying that my way is the only way but it has worked for me. It might give you some ideas though.
Sent from my iPad using Aquarium Advice