It's quite interesting that you have the mosses you do. To my understanding, Java and Willow are really the only two types of mosses commonly available that grow fully aquatic in their natural environment (and it's not a coincidence that these two are the easiest to keep). Because of this they don't require any special care and tend to do perfectly well an a wide variety of conditions, including low light, no co2, no fertilizer injections etc. This said, they can be grown emersed as well, but I find that java likes to be wetter than other mosses when grown emersed. The moss would probably grow on miracle grow, but mosses don't normally grow in dirt, they prefer something to attach to. I may worry about stagnancy from keeping it at the required moisture level and muddy water suffocating it from its light source, though all soils types are different, often even within the same brand. Where I do find moss growing in soil naturally, I've found the soil often has a high clay content, which functions differently than what I think of as Miracle Gro soil (think structural stability, water retension, amount and state of organics etc).
I'd say you're best off with just doing a normal submerged setup with this tank. I would suggest leaving the tank bare-bottom (I know, the horror!) and tying bits of moss to small pieces of rock, then putting those along the whole bottom. Willow moss's growing habits make it the ideal moss for this method, and it should grow out into a nice bushy carpet so you won't be able to see the rocks. Moss walls are good ways to make maximum use of the sides of your tanks, and you can always throw driftwood branches (or scuffed up PVC) in there with moss tied to them for even more growing space.
Riccia is different from the other two mosses you mentioned. It is actually a type of bog liverwort rather than a moss. This plant is considered to need high lighting and co2 supplementation to do well in the aquarium, as well as tied down somewhat obsessively with fishing line and trimmed so that the mass of the plant does not come off of the rock and float to the surface- it doesn't attach well to things when it's submerged. But the good news is, you can just let it do what it does best! Just throw it into your tank after it's set up and let it float. It should start to grow into a new floating mat on the surface. When grown as it's naturally evolved to do, I find that riccia does quite well in moderate or even low lighting, though others may have different experiences. If you want to control its growth more or for some reason it isn't matting on its own, rig one of those green dish scrubbies by tying some styrofoam to either side to form a floating raft so that the top is just at or just below the surface of the water. Just place your riccia (thinly) on top of this, and it should attach and start matting from there. Watch out, you should have to remove it so it doesn't block out your tank's light, as the mat will be quite thick.
best of luck