By "live plants" I assume you mean macro algae species. For these it is not necessary to use any mud or dirt or similar product. They do not absorb nutrients through their "roots". These root like structures are called holdfasts and only anchor the plant.
If your going to grow macro algae it is best done in a separate tank or refugium that is apart from the main display tank. Some of these algae species can get out of control fast and overcome corals your trying to grow. That being said, you can keep macro algaes in the main tank, but you really need to keep an eye on them.
The use of Miracle Mud is not something I would recommend. It is extremely expensive and had not been demonstrated to be better than anything else. As for the other muds out there, I would tend to not use them if I wanted typical SPS and LPS corals. I feel that mud, while it has some advantages, also has a lot of disadvantages. Corals require very high quality water, and this can be harder to reach if your using mud in the system. That being said, there are people that do use mud based refugiums and have excellent results.
Since you want to have corals, I would go with comparatively few fish, and keep most of them on the small size. I would add a few fish first and run the tank for a few months before I added a lot of corals.
Your also going to have to make some choices as to the types of corals you want to have. While many people do mix them, you are often better off keeping mostly soft corals or mostly LPS and SPS corals. I tend to like soft corals because they are very easy to keep and frag. They are also less demanding than many SPS corals.
With corals it is important to read up on the species before you purchase it. Some a lovely to look at but difficult to keep alive any length of time.
