Cute set up, looks like your newts will be happy once you get some plants in there! What kind of newts specifically are you planning on getting? I have had excellent luck with java moss, it provides an excellent cushion over the gravel and will grow pretty much anywhere. Make sure the species you get cannot swallow those rocks in case of impaction - its not a fun experience for the animal or the owner. Pothos is another very hardy plant that gorws well in water and planted in soil should you decide to go that route. Hygrophilia is another good choice, and I have used small banana plants scattered along the bottom to add a unique touch. However, I use a sand substrate so I am not sure how well they would do on a gravel base.
Check out Jennewt's Plant Page, she has some excellent photos and descriptions of each specimens growing requirements and optimal temperature range. This will be a factor in deciding which plants will thrive in your little paradise and which will fade away. The Vivariums and Enclosures forum also has some excellent suggestions, and there is a separate subsection for Plants in Vivariums as well. I hope you find some good inspiration, and good luck with the rest of your construction!