It is so much easier when you have 2 tanks, this will be no prob:
1. Setup new tank as desired, and enough new water to make up any volume difference between your new tank & old, get this oxygenated & heated.
2. Same day as move, or day before, move over and setup lighting
3. Drain all existing water into 5g buckets, and rubbermaids, don't go crazy on rubbermaid size, they get heavy quikly, but I found 20g ones filled 1/2 full was manageable with 2 people once they are filled some live rock each.
4. Put live rock & critters/corals into the same rubbermaids with your tank water. The tub(s) with critters/corals throw powerhead(s) & heater(s) in there.
5. Transport! If you are going a long distance buy a cheap 400w or even less power inverter for your vehicle, to keep the powerhead & heater going during the trip. If it is a short trip, dive fast.
6. Unload, dump your new water in, let it mix & come to temperature, all the while keep your rubbermaid(s) with live critters happy with a heater & powerhead.
7. Install critters, and voila!
Other tips:
1. To get your critters out, lower the water volume to a few inches, then the fish are easy to get without stressing them out chasing them with a net all over the place
2. If you are transporting a sandbed, depending on age & detrius contect you might want to rinse out a large portion thoroughly or else you will be releasing a lot of trapped junk in to you new system, and might get a spike. I have rinsed in tap water without any problems, no spikes even with 6" sandbeds in 100g+ tanks.
3. Don't turn your lighting on for the first day or two