I would at least remove the water down to the sand level. You put a lot of stress on the tank when you pick it up with the weight of water and rock. If you are careful I think you could get away with leaving the rock in the tank and maybe 2" of water for the fish, but i wouldn't leave a full 1/4 of the tank with water.
5 gallon buckets with lids work great for moving the water, rock and fish if you decide to remove them. If you decide to remove the rock and fish first half fill a couple of buckets with water from the tank and then place rock in the buckets. Keep one bucket half full of only water, no rocks, for the fish. After you have the rocks and most of clean water out of the display tank, catch the fish. Have plenty of pre-mixed, aerated, heated water on hand. Lastly disconnect as much plumbing and electrical as necessary for the move. Move the tank to the new location, get the plumbing and electrical reconnected. Place your rocks to your liking, add the sand and then the old water. Top off the tank with new saltwater. Turn on the pumps, heaters and the rest of your equipment. Once things are up and running, add the fish. The process always takes me longer than I think, plan on a full day.