It's a 10 gallon with a whisper filter that came out of my already cycled tank. The inhabitants are 1 bulldog pleco, 2 mystery snails, 4 2 week old platy fry, and 4 5 day old balloon molly fry.
If i was you, i would put some sand in, and some slate and bogwood for the plec to have some privacy, maybe a couple more plants, and i think a black background would be good
Make sure that internal filter dont suck up the fry
If it was my tank I would just add some caves, a few pieces of wood, and floating plants. I don't think the pleco needs gravel or sand. I like to stay simple with fry and hospital tanks, and it is much easier to keep a bare bottom tank.
Some Plecs like to bury themselves in the sand. It is a choice to make regarding substrate or not. I like substrate.
Yes, playsand is often recommended.
I like the slightly heavier sand at my lps. But I use something else for planted tanks as the bottom fish always dig everything up that is planted in sand.