Cazy if you still need help, I can try my best
I have gravel, because it seems to me for the plants to be easily rooted into the ground, and a lot of my plants never floated up onto the top
Also, if you were to have some plants say amazon swords, and other types of strong plants. Then I suggest you use larger gravel.
If you were to have some type of fishes say flounder tongues, then you will need a lot of sand, like fine sand, because they need a lot of deep space to bury themselves into the ground.
Stingrays, need a lot of sand too. Regular fishes that are usually on the top, or during the middle, will still be alright, since they don't really need to worry about anything...
Plecos will be fine too.