The first time I moved my tanks, I went out and bought a bunch of Homer buckets at home depot with lids. I fill the buckets with base rock and live rock from my aquariums.Then, I fill another bucket (or 5) for fish/mantis shrimp with water then catch the fish since all the rocks are out now

. Then I grab all the related corals so softies such a s zoas go in the same tupperware container then you float that container in the bucket with the rocks so it stays warmer longer. more delicate corals like birdsnests get their own container. it's pretty simple.
Once everything is out of the aquarium(s) I take a towel and place it on the sand bed to keep it wet, not moist, wet. I DO NOT recommend replacing the sand. There are way too many important organisms in the sand. also... "live sand" you buy at the store is a waste of money and is far from "live" and will not be as beneficial to you as leaving the old sand in.
always keep everything inside the cabin of the vehicle. I only haul my aquariums in the back of the truck if it is warm outside. do not attempt this in the winter. the sand, and tank glass will be so cold, that it will take you 6 hrs to warm up the new tank water. there are ways around this, but whatever. make it easy on yourself.
Also, I use ALL NEW saltwater. You might be able to save 50% of your old water but it should not have anything transported in it aka rock, fish. corals etc. I suggest using all new water.
Plan it out and give yourself lots of time. It usually takes me by myself 3 hours to break down and 3 hours to put it back up.
I have a 20g long SW, 6.6g fluval chi SW, 10g FW, 2.5g betta (that's a joke to move compared to SW), and a 5.5g mantis tank SW
if you have questions lmk