When I moved all my corals and fish from a 180 into the 240 I have now, I borrowed a couple 100 gallon stock tanks and bought a 6' diameter plastic swimming pool.
I pulled all the fish and corals out of the 180 and put them in the containers, which all had heaters and powerheads. The plastic swimming pool was used for the most delicate corals and fish. Once everything was moved into the temp containers, I took my time setting up the new tank to make sure it was perfect. I also had the new tank up and running with freshwater in my garage for a week or so before hand with all the pumps, closed loop, skimmer running, just to make sure it all worked.
I did have my living room messed up for 2 days.