I would use lava rock or clay pebbles instead of soil for the plants. The plants roots are better oxygenated and drain better.
Lava rock has names such as Eco-complete, CaribSea, Flourite. Clay pebbles sells by names such as LECA and Hydroton.
Check out the planted HOB thread for plants,
Use river sand with some sections of play sand for the pygmies in the tank. Sand tanks help with denitrification also.