I know for hardscape you can use fishing wire. Just lay the moss on the driftwood or whatever and tie the wire around it. After a few weeks you can cut the wire off because the moss should adhere to the object. I just leave my wire on.
Java moss does not have a rhizome, you might be thinking of java fern. Java moss wont really grow as a carpeting plant. Many people just tuck it between rocks or glue/tie it to decor and let it spread.
java moss is better for shrimp. Shrimplets also love it for feeding. Anubias can be glued or tied to any decor. You can also bury the roots in the substrate but the rhizome has to be exposed to the water.
One of the best things about Cherry Shrimp is that there's very little that they won't eat so it's easy to give them lots of variety. As well as that, they eat biofilm and algae that just grows naturally on surfaces.
10 would work. But read up on shrimp they are not easy. They need a well established tank with algae and bio-film. Expect to lose some. They can have problems when moved to a new tank. And if you succeed they will than reproduce and you could have a hundred in there.