hrm, I would definitely do the dirt with pool filter sand cap then, I think its the best bang for the buck and it can last for years.
General aquascaping advise though, before we talk about where to put plants, get some ideas for a hardscape (i.e. the rocks and driftwood that you want to use) because once you put your hardscape in, it will be easier to see how and where you want to put your plants. It also helps because your mosses and java fern (oh, forgot to mention anubias works as well) will be placed onto the hardscape and not into the substrate (its how these plants are supposed to grow). Random, another cool plant would be any of the crypt species, whichever ones float your boat. Wendetii is easy to find and comes in lots of color variations, but there are some other more exotic things out there as well.
Also, get a korelia pump or some other sort of pump, since in a tank that big you are going to be wanting as much water flow as you can get. I'd maybe ask someone more experienced with larger planted tanks about what pump specifically would work well for your scenario.