I love this set up but think the frogs (and you!) would love it much more if it had sand substrate. It gives them a softer landing area after their mad dash to the surface for a breath of air.

In my opinion, I would leave the lovely large rock set up you have and plant around it. It would really give your tank a great look. Plants you should check out are Anubis, Wisteria, Amazon Sword, Java Fern, Banana Plant....they are all very simple to keep and undemanding. They also help out immensely with water quality.