The substrate is an important part of the aquarium interior because a lot of animals dig in the ground to search for food. The plants also need a safe hold and have to absorb the food in the ground through their roots. Digging fish definitely need a substrate which is not sharp-edged. Undergravel heating can only be recommended for medium-fine to coarse substrates because water circulation cannot really build up in very fine substrates.
Rinse the substrate with tap water to remove any abrasion caused in transit. Put substrate on the nutrient substrate (JBL AquaBasis) to promote the plant growth (for vigorous plant roots approx. 6-8 cm).