I would suggest that you make an effort to keep 15 or 20 gallons of water so as not to stress the fish. The first thing you should do when you start breaking the tank down is to drain water into your transport containers. Do this first! Sometimes when you wait until the end you will find that you have stirred up detritus into the water column. I usually just syphon from the top of the water column for the water I plan to keep in a move.
Wrap your live rock in wet newspaper to keep it moist during your move. I bet if you ask the LFS
you deal with that they will have some spare styrophom collers for you to borrow to transport the live rock.
Personally, I would leave the sand on the bottom of the tank. I dont' disturb the substrate during a move. It will be heavy, but is ultimately your best bet.
When you arrive at your new location, first add the rock back to the tank. Then add the water which you saved. Add another 20 gallons of water (which you could have mixed ahead of time at the new location). Then add fish. You can now use your empty buckets to mix new SW
. Wait a few hours and then add the final 20 - 30 gallons of water.
I have moved 7 times during my fishkeeping years and have had multiple SW
tanks to move each time. This is my technique which I have found works well. Hopefully you find something helpful.