Don't be ever afraid to ask questions (Even the very, very basic ones) on this forum, it's somewhere for you to learn about them!
Here are the answers to your questions:
1. Generally, mosses do not require gravel or soil. You can simply tie them on bogwoods and rocks. It doesn't really relate to the nutrient content of your tank. Mosses can grow very well in an uncycled tank as well as a normal one.
2. It depends how you want to "use" it for. You can simply let it float, because after a few hours, the moss will eventually sink to the bottom of the tank. You can anchor them down if you like, or simply tie them on rocks or bogwoods.
3. You should still regularly clean the bottom of your tank, but I think you can do it less often. Mosses wouldn't really suffocate another one if they are given enough space to grow.
Hope all these helps
Unlimitedfishboy