The sand/gravel setup is fine for plants, no worries there, although you will need more as I'll mention below.
The plant I'm fairly certain is a Dracaena, and they are not true aquatic plants. It will live for a few months completely submerged (underwater), but eventually it is going to rot.
I would suggest sword plants, Echinodorus is the scientific name for the genus, and there are many different types. They grow well in all but the hardest water, and under low/moderate light. They are native to South and Central America so your Corydoras and livebearers would feel right at home. You will need a deeper substrate, whether sand or gravel, as swords have extensive root systems. [The Dracaena will need more too, but as it is not going to last long I'd concentrate on the swords.] A depth of 2 inches minimum, sloped up to 3 inches or 4 inches where the plants are planted, works fine.
A piece or two of bogwood would look nice, and Corydoras love wood to graze over, plus it can be arranged to provide shelter which makes them feel less "open". Small pieces of wood can also help build up deeper areas for the plants.