If you can put one above the tank, it will provide fauna to the display tank. Your fish and corals will enjoy the extra food.
You can put sand in it or go barebottom. A clump of cheato is what most people use. The grape caulerpa works also but can also crash and release everythign it absorbed.
Feed the fuge with a small powerhead or similar pump. (a few hundred gallons an hour is plenty). Light it on a revers cycle from your main display and it will help stabilize PH during the evening hours.
That is the basics.... search around RC for a little while, and you will be able to come up with some more specific questions.
Bean