Do I NEED to have sand??

You will be fine with the gravel. I'm not fond of white substrate as I prefer darker colors. I have sand in some of my tanks, gravel in some, and bare bottom in others. Most fish don't care. The eartheaters (Geophagus, etc..) will prefer the sand though. The mbuna and peacocks don't care as long as they can clear a flat surface if they decide to breed. They are mouth brooders so they only need the flat surface for a short time.

Yes you don't need to have sand. I have gravel in all my tanks tanks(except my shell dweller tank).

But with white gravel you should know that it will quickly loose its ncie whiteness and becomes dirty looking and may even turn a bit green with algae. I prefer natural or darker gravels as they show the fish's color better and seems to make the fish feel more secure.

i have a tank thats 2/3 black sand and 1/3 white gravel. looks pretty nice and the earth eaters seems to like it. the sand is kindof a pain to keep clean looking. you have to float the syphon a little over the bottom or u end up with all your sand getting sucked up.

I recently moved my malawis to a tank with sand, and they're having a great time excavating. The "landscape" is constantly changing.

I have never noticed my fish getting cut up when moving the gravel around. But my gravel is rounded.

What do you mean cut up? My Africans have never gotten "cut up," but they always put safety first. (zing!)