I have one bicolor angel in my 10 gallon who gets along great with my Percula Clownfish. The people at my LFS told me that even in a bigger tank, it wouldn't be wise to put 2 or more dwarf angels together because they would fight over territories.
As for the crushed coral, I don't think it matters wether you use synthetic salt or real sea salt. However, I've read in other parts of this forum that using only crushed coral by itself can bring you problems later down the road. JMO though. Hope it helps!