I may be able to explain why a substrate is important, whether it is fine gravel or sand. This is the biological hub of the aquarium. There are many species of bacteria that will live in the substrate, feeding on the organics that accumulate there. The filter is your nitrification bacteria primarily, though this occurs in the substrate too. But there is so much more to bacteria than just the filter.
Floating plants are a very good idea, and should be included in most all freshwater tanks, with some exceptions. They shade light (which does affect forest fish), and help to keep the water quality good.
Unless you have a reason for the titles, meaning something the fish may need (spawning sites), I would not put them in the aquarium. Once you have the substrate, decor like chunks of wood and/or rock is better, depending what the particular fish species may need. The fish have environmental needs which should come first if they are to be healthy.
Byron.