If I remember correctly, aragonite sand is going to raise your pH. Use play sand or similar, this is fine for growing most plants.
First you need to decide what you want your tank to look like, pictures from the internet are good. Then decide if you want to go the high tech route, CO2, strong lights, ferts, or low tech, moderate lighting and few additional ferts. With your current setup, you'd be restricted to moss, java fern, Anubias and similar slow growing plants.
And in regards to the filter, ditch the carbon for a mechanical media such as sponge or filter wool.