I much prefer regular plants. If you want to be able to move the plants around a lot, potted plants are ok. The problem is the felt/wool stuff (don't know exactly what it is) they are potted in will start to deteriorate and rot. When I order plants and they come in as potted plants, I take them out, remove all the packing and plant them in the substrate.
for plants, the substrate should be about 1 1/2 to 2 inches for gravel, not sure about sand.
Yeah, just take the pots and rock wool off, and plant the plant! Be careful with the roots however.