This is a question best asked in one of the general forums, where you will get a greater diversity of opinions, and help form more different people.
A brief answer here though:
You could keep *many* different sorts of corals with these fish, and your coral choice is going to be more a function of tank size, lighting, water flow, etc. The clownfish might pester and bother some large polyped stony corals or some large soft corals by trying to use them as anemone-like hosts...or it might not...or if it does, the corals may or may not be bothered by the clownsfish's attention (this is hard to predict).
I like several inches of fine sand...maybe 4 inches?
Amount of rock will vary depending on a variety of factors, including the type of rock. Don't fill the tank with rock to the top...leave room for coral growth...you will need this space for growth sooner than you might imagine. I am coming to prefer a bit less rock than what some might recommend, in order to leave a bit more open space in the tank. However, I think your best bet is to ask folks in one of the other forums for their opinions on this. You will get good advice (and personally I'm not sure what poundage of rock to recommend... in recent years I have not kept track of the weight of rocks in my tanks..I tend to go with what "looks right" to me).
Again, take this question to one of the forums where you can get good advice from a variety of different people.
Also, if there is a reef aquarium club where you live, the members of that group should be able to help you A LOT. Seek out these local reefkeepers, and if possible, visit their tanks to see their setups. Seeing several established reef tanks in operation is VERY useful when first starting out (and most of the tanks in aquarium shops are not useful in this regard because the livestock does not stay long, and you can't really judge the success of the tank).