all of your questions will be answered by one question ...
what type of corals are we talking about fragging ?? soft coral and LPS ... will be forgiving of each other and can share a tank.
SPS,
IMHO, need to be kept in a separate system.
what size tank ... as shallow as you can find, usually something like a 40breeder works for everyone.
lighting ... depends on what you are going to be cutting on. i would use what ever you have on the display tank that they will be coming from. keep away from windows, windows in most cases = algae blooms.
racks ... you can get the racks at home depot or lowes in the lighting department. it is called florescent light diffuser. it is about $10 per 4x2 sheet here and you can cut it to you desired size with a pair of side cutters.